EXHIBIT 10.15

PROMISSORY NOTE

DEFINED TERMS



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|Execution Date: July 29, 2010                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |  | City and State of Signing:
Newport Beach, California                                                                                                                                                                                                                                                     
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|Loan Amount: Three Hundred Fifty Million and No/100 Dollars ($350,000,000.00)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |  | Interest Rate: 4.25%
per annum                                                                                                                                                                                                                                                                           
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|Borrower: KBSII 300 North LaSalle, LLC, a Delaware limited liability company                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
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|Borrowers Address:                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |  | c/o KBS Capital Advisors LLC
620 Newport Center Drive, Suite 1300 Newport
Beach, California 92660                                                                                                                                                                                                        
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|Holder: Metropolitan Life Insurance Company, a New York corporation                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
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|Holders Address:                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |  | Metropolitan Life Insurance Company
10 Park Avenue Morristown, New Jersey
07962                                                                                                                                                                                                                          
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |  | Attention:                                                                                                                                                                                                                                                                                                |  | Senior Vice President
Real Estate Investments Re: 300 N.
LaSalle
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|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |  | With a copy to: 
Metropolitan Life Insurance Company 125 S.
Wacker, Suite 1100 Chicago, Illinois 60606
Attention:         Director                                                                                                                                                                       
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|Maturity Date: August 1, 2015                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |  | Advance Date: The date funds are disbursed to Borrower.                                                                                                                                                                                                                                                  
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|Interest Only Period: Three (3) year period, commencing on the Execution Date and continuing through August 1, 2013.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |  | Principal and Interest Installment Date: September 1, 2013                                                                                                                                                                                                                                               
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|Monthly Installment: Shall mean, as applicable: (i) September 1, 2010 and the first day of each month thereafter through and including August 1, 2013,
One Million Two Hundred Thirty-Nine Thousand Five Hundred Eighty-Three and 33/100ths Dollars ($1,239,583.33) shall be paid, representing the payment of interest only on the Loan Amount at the Interest Rate (the Interest Only
Installment); and (ii) commencing with the Principal and Interest Installment Date and ending on the Maturity Date: equal monthly installments of principal and interest each in the amount of One Million Seven Hundred Twenty-One Thousand |  | Permitted Prepayment Period: During the 90 day period prior to the Maturity Date, Borrower may prepay the Loan without a Prepayment Fee on 30 days prior written notice. In
addition, commencing on February 1, 2013, Borrower may prepay the Loan with a Prepayment Fee on 30 days prior written notice.



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|Seven Hundred Eighty-Nine and 62/100ths Dollars ($1,721,789.62) (each a Principal and Interest Installment).  The Principal and Interest Installments payable after the Interest Only
Period are based upon an amortization period of 30 years.  Interest for
the period of time between the Advance Date and July 31, 2010 shall be paid by Borrower on the Advance Date.                                                                                                                                                                                                                                                                                                                                                                                                        |  |                                                                                                  
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|Liable Party: KBS REIT PROPERTIES II, LLC, a Delaware limited liability company                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
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|Addresses of Liable Party:                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |  | c/o KBS Capital Advisors LLC
620 Newport Center Drive, Suite 1300 Newport
Beach, California 92660
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|Late Charge: An amount equal to four cents ($.04) for each dollar that is overdue.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
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|Default Rate: An annual rate equal to the Interest Rate plus four percent (4%).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
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|Note: This Promissory Note. Mortgage: Mortgage, Security Agreement, and Fixture Filing dated as of the Execution Date executed by Borrower for the benefit
of Holder. Loan Documents: This Note, the Mortgage and any other documents related to this Note and/or the Mortgage and all renewals, amendments, modifications, restatements and extensions of these documents. Guaranty: Guaranty dated
as of the Execution Date and executed by Liable Party. Indemnity Agreement: Unsecured Indemnity Agreement dated as of the Execution Date and executed by Borrower in favor of Holder. The Unsecured Indemnity Agreement and Guaranty are not Loan
Documents and shall survive repayment of the Loan or other termination of the Loan Documents in accordance with their terms.

FOR VALUE RECEIVED, Borrower promises to pay to the order of Holder at Holders Address or such other place as
Holder may from time to time designate, the Loan Amount with interest payable in the manner described below, in money of the United States of America that at the time of payment shall be legal tender for payment of all obligations.

Capitalized terms which are not defined in this Note shall have the meanings set forth in the Mortgage.

1. Payment of Principal and Interest. Principal and interest under this Note shall be payable as follows:

(a) Interest on the funded portion of the Loan Amount which shall accrue at the Interest Rate from the
Advance Date through the last calendar day of the month in which the Advance date occurs shall be paid by Borrower in advance on the Advance Date;

(b) Commencing on September 1, 2010 and continuing on the first day of each calendar month thereafter, to and
including the first day of the calendar month immediately preceding the Maturity Date, Borrower shall pay the Monthly Installment; and



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(c) On the Maturity Date, a final payment in the aggregate amount of the
unpaid principal sum evidenced by this Note, all accrued and unpaid interest, and all other sums evidenced by this Note or secured by the Mortgage and/or any other Loan Documents as well as any future advances under the Mortgage that may be made to
or on behalf of Borrower by Holder following the Advance Date (collectively, the Secured Indebtedness), shall become immediately payable in full.

Borrower acknowledges and agrees that a substantial portion of the original Loan Amount shall be outstanding and due on
the Maturity Date.

Interest shall be calculated on the basis of a thirty (30) day month and a three
hundred sixty (360) day year, except that (i) if the Advance Date occurs on a date other than the first day of a calendar month, interest payable for the period commencing on the Advance Date and ending on the last day of the month in
which the Advance Date occurs shall be calculated on the basis of the actual number of days elapsed over a 365 day or 366 day year, as applicable, and (ii) if the Maturity Date occurs on a date other than the last day of the month, interest
payable for the period commencing on the first day of the month in which the Maturity Date occurs and ending on the Maturity Date shall be calculated on the basis of the actual number of days elapsed over a 365 day or 366 day year, as applicable.

2. Application of Payments. At the election of Holder, and to the extent permitted by law, all
payments shall be applied in the order selected by Holder to any expenses, prepayment fees, late charges, escrow deposits and other sums due and payable under the Loan Documents, and to unpaid interest at the Interest Rate or at the Default Rate, as
applicable. The balance of any payments shall be applied to reduce the then unpaid Loan Amount.

3.
Security. The covenants of the Mortgage are incorporated by reference into this Note. This Note shall evidence, and the Mortgage shall secure, the Secured Indebtedness.

4. Late Charge. If any payment of interest, any payment of a Monthly Installment or any payment of a required
escrow deposit is not paid within 7 days of the due date, Holder shall have the option to charge Borrower the Late Charge. The Late Charge is for the purpose of defraying the expenses incurred in connection with handling and processing delinquent
payments and is payable in addition to any other remedy Holder may have. Unpaid Late Charges shall become part of the Secured Indebtedness and shall be added to any subsequent payments due under the Loan Documents.

5. Acceleration Upon Default. At the option of Holder, if an Event of Default occurs or if Borrower fails to pay
any sum specified in this Note within ten (10) days of the date of written notice of such failure from Holder to Borrower, the Secured Indebtedness, and all other sums evidenced and/or secured by the Loan Documents, including without limitation
any applicable prepayment fees (collectively, the Accelerated Loan Amount) shall become immediately due and payable.

6. Interest Upon Default. The Accelerated Loan Amount shall bear interest at the Default Rate which shall never
exceed the maximum rate of interest permitted to be contracted for under the laws of the State. The Default Rate shall commence upon the occurrence of an Event of Default and shall continue until all defaults are cured.



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7. Limitation on Interest. The agreements made by Borrower with
respect to this Note and the other Loan Documents are expressly limited so that in no event shall the amount of interest received, charged or contracted for by Holder exceed the highest lawful amount of interest permissible under the laws applicable
to the Loan. If at any time performance of any provision of this Note or the other Loan Documents results in the highest lawful rate of interest permissible under applicable laws being exceeded, then the amount of interest received, charged or
contracted for by Holder shall automatically and without further action by any party be deemed to have been reduced to the highest lawful amount of interest then permissible under applicable laws. If Holder shall ever receive, charge or contract
for, as interest, an amount which is unlawful, at Holders election, the amount of unlawful interest shall be refunded to Borrower (if actually paid) or applied to reduce the then unpaid Loan Amount. To the fullest extent permitted by
applicable laws, any amounts contracted for, charged or received under the Loan Documents included for the purpose of determining whether the Interest Rate would exceed the highest lawful rate shall be calculated by allocating and spreading such
interest to and over the full stated term of this Note.

8. Prepayment. Borrower shall not have the
right to prepay all or any portion of the Loan Amount at any time during the term of this Note except as expressly set forth in the Defined Terms. If Borrower provides notice of its intention to prepay, the Accelerated Loan Amount shall become due
and payable on the date specified in the prepayment notice; provided, however, that no more than two (2) times in any twelve (12) month period, Borrower shall have the right (at no cost or expense to Borrower) to revoke any notice to
Holder of Borrowers notice to prepay upon five (5) days prior written notice to Holder.

9.
Prepayment Fee.

(a) Any tender of payment by Borrower or any other person or entity of the Secured
Indebtedness, other than as expressly provided in the Loan Documents, shall constitute a prohibited prepayment. If a prepayment of all or any part of the Secured Indebtedness is made following (i) an Event of Default and an acceleration of the
Maturity Date, (ii) the application of money to the principal of the Loan after a casualty or condemnation, or (iii) in connection with a purchase of the Property or a repayment of the Secured Indebtedness at any time before, during
or after, a judicial or non-judicial foreclosure or sale of the Property, then to compensate Holder for the loss of the investment, Borrower shall pay an amount equal to the Prepayment Fee (as hereinafter defined). Notwithstanding the foregoing, so
long as Borrower makes a good faith effort to recover any Prepayment Fee which would be due as a result of a casualty or condemnation, from the insurer in the case of a casualty or from the condemning authority, then the Prepayment Fee due as a
result of the casualty or condemnation shall be waived except to the extent recovered by Borrower.

(b) The
Prepayment Fee shall be the greater of (A) the Prepayment Ratio (as hereinafter defined) multiplied by (x  y), where (x) is the present value of all remaining payments of principal and interest including the
outstanding principal due on the Maturity Date, discounted at the rate which, when compounded monthly, is equivalent to the Treasury Rate plus 0.35% compounded semi-annually, and (y) is the amount of the principal then outstanding, or
(B) one percent (1%) of the amount of the principal being prepaid.



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(c) The Treasury Rate shall be the annualized yield on
securities issued by the United States Treasury having a maturity equal to the remaining stated term of this Note, as quoted in the Federal Reserve Statistical Release [H. 15 (519)] under the heading U.S. Government Securities -
Treasury Constant Maturities for the date which is five (5) Business Days prior to the date on which prepayment is being made. If this rate is not available as of the date of prepayment, the Treasury Rate shall be determined by
interpolating between the yield on securities of the next longer and next shorter maturity. If the Treasury Rate is no longer published, Holder shall select a comparable rate. Holder will, upon request, provide an estimate of the amount of the
Prepayment Fee two weeks before the date of the scheduled prepayment. A Business Day is a day on which both the Holder and the bond market are conducting normal business operations.

(d) The Prepayment Ratio shall be a fraction, the numerator of which shall be the amount of principal
being prepaid, and the denominator of which shall be the principal then outstanding.

10. Waiver of Right
to Prepay Note Without Prepayment Fee. Borrower acknowledges that Holder has relied upon the anticipated investment return under this Note in entering into transactions with, and in making commitments to, third parties and that the tender of any
prohibited prepayment or any permitted prepayment which pursuant to the terms of this Note requires a Prepayment Fee, shall include the Prepayment Fee. Borrower agrees that the determination of the Interest Rate was based on the intent, expectation
and agreement (and the Interest Rate would have been higher without such agreement) of Borrower and Holder that the amounts advanced under this Note would not be prepaid during the term of this Note, or if any such prepayment would occur, the
Prepayment Fee would apply (except as expressly permitted by the terms of this Note). Borrower also agrees that the Prepayment Fee represents the reasonable estimate of Holder and Borrower of a fair average compensation for the loss that may be
sustained by Holder as a result of a prepayment of this Note and it shall be paid without prejudice to the right of Holder to collect any other amounts provided to be paid under the Loan Documents.

EXCEPT AS EXPRESSLY OTHERWISE PROVIDED IN THIS NOTE OR IN THE OTHER LOAN DOCUMENTS, BORROWER EXPRESSLY (A) WAIVES
ANY RIGHTS IT MAY HAVE UNDER ILLINOIS LAW TO PREPAY THIS NOTE, IN WHOLE OR IN PART, WITHOUT FEE OR PENALTY, UPON ACCELERATION OF THE MATURITY DATE OF THIS NOTE, AND (B) AGREES THAT IF, FOR ANY REASON, A PREPAYMENT OF THIS NOTE IS MADE, UPON OR
FOLLOWING ANY ACCELERATION OF THE MATURITY DATE OF THIS NOTE BY HOLDER ON ACCOUNT OF ANY DEFAULT BY BORROWER UNDER ANY LOAN DOCUMENT, INCLUDING BUT NOT LIMITED TO ANY TRANSFER, FURTHER ENCUMBRANCE OR DISPOSITION WHICH IS PROHIBITED OR RESTRICTED BY
THE MORTGAGE, THEN BORROWER SHALL BE OBLIGATED TO PAY CONCURRENTLY THE PREPAYMENT FEE SPECIFIED IN SECTION 9. BY EXECUTING THIS NOTE, BORROWER AGREES THAT HOLDERS AGREEMENT TO MAKE THE LOAN AT THE INTEREST RATE AND FOR THE TERM SET FORTH IN
THIS NOTE CONSTITUTES ADEQUATE CONSIDERATION FOR THIS WAIVER AND AGREEMENT.



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11. Liability of Borrower. Upon the occurrence of an Event of
Default, except as provided in this Section 11, Holder will look solely to the Property and the security under the Loan Documents for the repayment of the Loan and will not enforce a deficiency judgment against Borrower. However, nothing
contained in this section shall limit the rights of Holder to proceed against Borrower and/or the Liable Party (but not any of their respective constituent members or partners, direct or indirect), if any, (i) to enforce any Leases entered into
by Borrower or its affiliates as a tenant under any of the Leases; (ii) to recover damages for fraud, material misrepresentation, material breach of warranty or intentional material physical waste; (iii) to recover any Condemnation
Proceeds or Insurance Proceeds or other similar funds which have been misapplied by Borrower in violation of the Loan Documents or which, under the terms of the Loan Documents, should have been paid to Holder; (iv) to recover any tenant
security deposits, tenant letters of credit or other deposits or fees paid to Borrower in connection with the Property or prepaid rents for a period of more than 30 days after an Event of Default occurs; (v) to recover Rents and Profits
received by Borrower after the first day of the month in which an Event of Default occurs and prior to the date Holder acquires title to the Property which have not been applied to the Loan or in accordance with the Loan Documents to operating and
maintenance expenses of the Property; (vi) to recover solely from Borrower (and not any Liable Party with respect to this Section 11(vi)) damages, costs and expenses arising from, or in connection with Article VI of the Mortgage pertaining
to hazardous materials or the Indemnity Agreement; (vii) to recover all amounts due and payable pursuant to Sections 11.06 and 11.07 of the Mortgage, excluding any amount expended by Holder in connection with the foreclosure of the Mortgage;
(viii) to recover costs and damages arising from Borrowers failure to pay Premiums or Impositions in the event Borrower is not required to deposit such amounts with Holder pursuant to Section 2.05 of the Mortgage; and/or (ix) to
recover damages arising from Borrowers failure to comply with Section 8.01 of the Mortgage pertaining to ERISA.

The limitation of liability set forth in this Section 11 shall not apply and the Loan shall be fully recourse to the
Borrower and to the Liable Party (but not their respective constituent members or partners, direct or indirect) in the event that prior to the repayment of the Secured Indebtedness, Borrower commences a voluntary bankruptcy or insolvency proceeding
or is involved in a collusive involuntary bankruptcy or insolvency proceeding which is not dismissed within 120 days of filing. In addition, this agreement shall not waive any rights which Holder would have under any provisions of the U.S.
Bankruptcy Code to file a claim for the full amount of the Secured Indebtedness or to require that the Property shall continue to secure all of the Secured Indebtedness.

Notwithstanding the foregoing, the Loan shall be fully recourse to the Borrower and the Liable Party (but not their
respective constituent members or partners, direct or indirect), in the event there is a voluntary Transfer or voluntary Secondary Financing except as permitted in the Loan Documents or otherwise approved in writing by Holder. For purposes of this
paragraph, Transfers shall only refer to transfers of ownership of the Property or of ownership interests in entities directly or indirectly owning the Property.

12. Waiver by Borrower. Except as expressly otherwise provided in this Note or in the other Loan Documents,
Borrower and others who may become liable for the payment of all or any part of this Note, and each of them, waive diligence, demand, presentment for payment, notice of nonpayment, protest, notice of dishonor and notice of protest, notice of intent
to accelerate and notice of acceleration and specifically consent to and waive notice of any



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amendments, modifications, renewals or extensions of this Note, including the granting of extension of time for payment, whether made to or in favor of Borrower or any other person or persons.

13. Exercise of Rights. No single or partial exercise by Holder, or delay or omission in the exercise
by Holder, of any right or remedy under the Loan Documents shall waive or limit the exercise of any such right or remedy. Holder shall at all times have the right to proceed against any portion of or interest in the Property in the manner that
Holder may deem appropriate, without waiving any other rights or remedies. The release of any party under this Note shall not operate to release any other party which is liable under this Note and/or under the other Loan Documents or under the
Unsecured Indemnity Agreement.

14. Fees and Expenses. If Borrower defaults under this Note, Borrower
shall be personally liable for and shall pay to Holder, in addition to the sums stated above, the reasonable costs and expenses of enforcement and collection, including a reasonable sum as an attorneys fee. This obligation is not limited by
Section 11.

15. No Amendments. This Note may not be modified or amended except in a writing
executed by Borrower and Holder. No waivers shall be effective unless they are set forth in a writing signed by the party which is waiving a right. This Note and the other Loan Documents are the final expression of the lending relationship between
Borrower and Holder.

16. Governing Law. This Note is to be construed and enforced in accordance with
the laws of the State.

17. Construction. The words Borrower and Holder shall
be deemed to include their respective heirs, representatives, successors and assigns, and shall denote the singular and/or plural, and the masculine and/or feminine, and natural and/or artificial persons, as appropriate. The provisions of this Note
shall remain in full force and effect notwithstanding any changes in the shareholders, partners or members of Borrower. If more than one party is Borrower, the obligations of each party shall be joint and several. The captions in this Note are
inserted only for convenience of reference and do not expand, limit or define the scope or intent of any section of this Note.

18. Notices. All notices, demands, requests and consents permitted or required under this Note shall be given in
the manner prescribed in the Mortgage.

19. Time of the Essence. Time shall be of the essence with
respect to all of Borrowers obligations under this Note.

20. Severability. If any provision of
this Note should be held unenforceable or void, then that provision shall be deemed separable from the remaining provisions and shall not affect the validity of this Note, except that if that provision relates to the payment of any monetary sum,
then Holder may, at its option, declare the Secured Indebtedness (together with the Prepayment Fee) immediately due and payable.

[Remainder of page intentionally left blank; signature page immediately follows]



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IN WITNESS WHEREOF, Borrower has executed this Note as of the Execution
Date.



KBSII 300 NORTH LASALLE, LLC,a Delaware limited liability companyBy:

KBSII REIT ACQUISITION XIV, LLC,
a Delaware limited liability company, its sole memberBy:

KBS REIT PROPERTIES II, LLC,
a Delaware limited liability company, its sole memberBy:

KBS LIMITED PARTNERSHIP II,
a Delaware limited partnership, its sole memberBy:

KBS REAL ESTATE
INVESTMENT TRUST II, INC., a Maryland
corporation, general partnerBy:

/s/ Charles J. Schreiber, Jr.Name:

Charles J. Schreiber, Jr.Title:

Chief Executive Officer