<PAGE>

                                                                   EXHIBIT 10.15

                      THIRD MODIFICATION TO LOAN AGREEMENT

                                     between

                                ITT CORPORATION,

                    STARWOOD HOTELS & RESORTS WORLDWIDE, INC.

                         SLT REALTY LIMITED PARTNERSHIP,

                            STARWOOD HOTELS & RESORTS

                                       and

                    STARWOOD HOTELS & RESORTS HOLDINGS, INC.

                  ---------------------------------------------

                            Dated as of June 23, 2000

                  ---------------------------------------------

<PAGE>

            THIRD MODIFICATION TO LOAN AGREEMENT, dated as of June 23, 2000
(this "Agreement"), between ITT CORPORATION, a Nevada Corporation (the
"Borrower" or "ITT"), successor-in-interest to Starwood Hotels & Resorts
Worldwide, Inc., a Maryland corporation (the "Corporation"), and SLT REALTY
LIMITED PARTNERSHIP, a Delaware limited partnership (the "Lender" or "SLT
Realty"), STARWOOD HOTELS & RESORTS, a Maryland real estate investment trust
(the "Trust"), and STARWOOD HOTELS & RESORTS HOLDINGS, INC, an Arizona
corporation ("Starwood Holdings"). Unless otherwise defined herein, all
capitalized terms used herein shall have the respective meanings provided such
terms in the Loan Agreement, as amended, referred to below.

                                   WITNESSETH:

            WHEREAS, the Trust previously made a loan to the Corporation in the
maximum principal amount of up to $3,282,000,000 (the "Loan") pursuant to that
certain Loan Agreement, dated as of February 23, 1998 (as amended, supplemented
or otherwise modified from time to time, the "Original Loan Agreement"), which
Loan was assigned by the Trust to the Lender pursuant to that certain General
Assignment dated as of February 23, 1998 and is evidenced, inter alia, by that
certain Promissory Note, dated as of February 23, 1998 (the "Original Note");

            WHEREAS, the Corporation assigned its existing rights and
obligations under the Original Loan Agreement to the Borrower pursuant to that
certain Assignment and Assumption Agreement dated as of December 17, 1998;

            WHEREAS, in connection with the transactions contemplated under a
certain Loan Agreement dated as of January 27, 1999 (as amended from time to
time, the "CMBS Loan Agreement"), Borrower, the Sheraton Phoenician Corporation
and Lender entered into a certain Agreement of Severance of Note and
Modification of Deed of Trust, dated as of January 27, 1999 (the "Severance
Agreement"), pursuant to which the parties thereto agreed (i) to separate the
Original Note into two notes, one of which evidenced a portion of the
outstanding principal balance of the Original Note, with interest thereon, equal
to $2,489,467,038.25 (the "Mortgage Note") and the other of which evidenced the
remaining portion of the outstanding principal balance of the Original Note,
with interest thereon, equal to $210,000,000 (the "Substitute Note
(Phoenician)") and (ii) to amend a certain Deed of Trust, Security Agreement and
Financing Statement dated as of February 23, 1998 (the "Phoenician Deed of
Trust") to secure only the indebtedness evidenced by the Substitute Note
(Phoenician) (all of the foregoing being herein referred to as the "Phoenician
Note Transaction");

            WHEREAS, in connection with the transactions contemplated under the
CMBS Loan Agreement and the Phoenician Note Transaction, the parties thereto
agreed to modify the Original Loan Agreement by First Modification to Loan
Agreement dated as of January 27, 1999 (as modified, the "Loan Agreement") to
provide for, among other things, (i) the severance of the Original Note and the
modification of the Phoenician Deed of Trust, (ii) the extension of the Final
Maturity Date of the Loan to February 23, 2014 and, additionally, the further
extension of the Final Maturity Date of the Loan upon any extension of the
maturity date of the loan advanced under the CMBS Loan Agreement, and (iii) the
amendment of certain definitions under the Original Loan Agreement;

                                       1

<PAGE>

            WHEREAS, on or about April 27, 1999, the Corporation, ITT Sheraton
Corporation, Starwood Canada Corp. ("Starwood Canada"), Caesars World Inc.
("Caesars World"), Sheraton Desert Inn Corporation, Sheraton Tunica Corporation
("Tunica") and Park Place Entertainment Corporation ("Park Place") entered into
that certain Stock Purchase Agreement (as amended or modified from time to time,
the "Caesars Stock Purchase Agreement"), pursuant to which, inter alia, Park
Place agreed to purchase, and the Corporation and certain Subsidiaries of the
Corporation agreed to sell, (i) all of the outstanding shares of common stock of
each of Caesars World and Tunica and (ii) all of Starwood Canada's partnership
interests in and notes receivable from Metropolitan Entertainment Group, a
Canadian partnership, which partnership interests represent ninety-five percent
(95%) of the economic ownership interest therein, and (iii) the Halifax Sheraton
Hotel owned by Clocktower Hotel Limited Partnership, in each case, subject to
and in addition to all of the other matters described in the Caesars Stock
Purchase Agreement (all of the foregoing, together with the matters described in
the following paragraphs, being collectively referred to herein as the "Caesars
World Transaction");

            WHEREAS, certain real property assets relating to the Caesars World
Transaction (collectively, the "Caesars World Assets") secured the Mortgage
Note, and, as a condition to the consummation of the Caesars World Transaction,
the Caesars World Assets were required to be released from the collateral
security for the Mortgage Note;

            WHEREAS, in connection with the consummation of the Caesars World
Transaction and the release of the Caesars World Assets, the Corporation and ITT
agreed to (i) reduce the outstanding principal balance of the Mortgage Note by
$1,200,000,000 in order to prevent the Mortgage Note from being
undercollateralized after the release of the Caesars World Assets (the amount of
such reduction being referred to herein as the "Mortgage Reduction Amount"), and
(ii) consummate certain other transactions in connection therewith (all of the
foregoing, together with the next recital, being referred to herein,
collectively, as the "Caesars Mortgage Note Transaction");

            WHEREAS, in order to effectuate all of the foregoing, the
Corporation, the Trust, SLT Realty and ITT entered into a certain Agreement of
Severance of Note and Release of Security Instruments dated as of December
30, 1999, whereby the Mortgage Note was separated into two notes (the two notes
being referred to herein as the "New Mortgage Note" and the "Unsecured Note"),
so that (i) the principal amount of the New Mortgage Note was in an amount equal
to the balance of the Mortgage Note prior to the separation into two new notes,
less the Mortgage Reduction Amount, (ii) the outstanding principal amount of the
new Unsecured Note was equal to the Mortgage Reduction Amount, and (iii) the
aggregate outstanding principal amount of both the New Mortgage Note and the new
Unsecured Note immediately subsequent to the consummation of the Caesars
Mortgage Note Transaction was equal to the outstanding principal amount of the
Mortgage Note immediately prior to the consummation of the Caesars Mortgage Note
Transaction;

            WHEREAS, prior to the consummation of the transactions contemplated
under the Caesars Mortgage Note Transaction, the Mortgage Note was secured by,
inter alia, certain Mortgages (as defined in the Loan Agreement) (other than the
Phoenician Deed of Trust);

                                       2

<PAGE>

            WHEREAS, in connection with the transactions contemplated under the
Caesars Mortgage Note Transaction, the parties additionally modified the
Original Loan Agreement (as modified, the "Loan Agreement"), pursuant to that
certain Second Modification to Loan Agreement dated as of December 30,1999, to
provide for, among other things, (i) (a) the separation of the Mortgage Note and
(b) the modification of the Mortgages (other than the Phoenician Deed of Trust)
and the discharge and release of the liens of certain Mortgages from the Caesars
World Assets so that the remaining Mortgages secured only the New Mortgage Note
and all of the indebtedness evidenced thereunder, (ii) (a) the assignment of all
of Lender's right, title and interest in the Unsecured Note and all documents
and agreements in connection therewith to the Trust and (b) the subsequent
assignment of all of the Trust's right, title and interest in the Unsecured Note
and all documents and agreements in connection therewith to Starwood Holdings,
and the assumption by Starwood Holdings of all of such right, title and interest
and (iii) the amendment of certain definitions under the Loan Agreement;

            WHEREAS, Borrower has agreed to sell the hotel property known as the
"Desert Inn" (the matters contemplated under such sale being referred to herein
as the "Desert Inn Transaction") and, as a consequence of the Desert Inn
Transaction, Borrower has requested that the Lender release the Desert Inn from
the collateral security for the New Mortgage Note; and

            WHEREAS, in consideration for, and in connection with, the release
of the Desert Inn from the collateral security of the New Mortgage Note, the
parties hereto desire to modify the New Mortgage Note and the Loan Agreement
(but only with respect to provisions specific to the New Mortgage Note) to
provide for (i) the increase in the Interest Rate, only as applied to the New
Mortgage Note, from the current interest rate of eight and one half percent
(8.5%) per annum to ten percent (10%) per annum and (ii) the release of the
Desert Inn from the collateral security for the New Mortgage Note;

            NOW, THEREFORE, the parties hereto have agreed as follows:

            1. The parties hereto acknowledge and agree that the Interest Rate
of, and only as applied to, the New Mortgage Note is hereby modified and
increased from eight and one half percent (8.5%) per annum to ten percent (10%)
per annum.

            2. The parties hereto acknowledge and agree that (i) the lien of the
Mortgage(s) set forth on Exhibit A hereto shall be released and discharged from
such Mortgage(s) and (ii) the remaining Mortgages (other than the Phoenician
Deed of Trust) shall continue to secure the outstanding principal balance under
the New Mortgage Note, with interest thereon, equal to $1,289,467,038.25.

            3. The terms and provisions of this Agreement shall be binding upon
and inure to the benefit of the parties and their respective successors and
assigns.

            4. This Agreement shall be governed by and construed in accordance
with the laws of the State of New York without giving effect to principles of
conflicts of laws.

                                       3

<PAGE>

            5. This Agreement is limited as specified and shall not constitute a
modification, acceptance or waiver of any other provision of the Loan Agreement
or New Mortgage Note.

            6. This Agreement may be signed in any number of counterparts, each
of which shall be an original, with the same effect as if the signatures thereto
and hereto were upon the same instrument.

            7. The parties hereto acknowledge and agree that the name "Starwood
Hotels & Resorts" is a designation of the Trust and its trustees (as trustees
but not personally) under a Declaration of Trust dated August 25, 1969, as
amended and restated as of June 6, 1988 and as further amended and restated as
of January 6, 1999, and as the same has been or may be amended from time to time
thereafter, and that the parties hereto shall look solely to the Trust's assets
for the enforcement of any claims against the Trust, as the trustees, officers,
agents and security holders of the Trust assume no personal liability for
obligations entered into on behalf of the Trust, and their respective individual
assets shall not be subject to the claims of any person relating to such
obligations. The foregoing shall govern all direct and indirect obligations of
the Trust under this Agreement.

            8. The Lender and the Borrower acknowledge, agree and hereby
reaffirm that all rights of the Lender to receive any payments from the Borrower
under the New Mortgage Note and the Loan Agreement, as amended hereby, or under
any guarantees, mortgages, other types of security documents or otherwise are
and shall continue to be subject and subordinate in payment to the prior payment
in full, in cash, of all Senior Indebtedness (as defined in the Subordination
Agreement), to the extent, and in the manner set forth in the Subordination
Agreement. All of the terms, covenants and conditions hereof are hereby and
shall continue to be subordinate to all of the terms, covenants and conditions
of the Senior Indebtedness. The foregoing shall apply, notwithstanding the
availability of other collateral to the Senior Creditors (as defined in the
Subordination Agreement) or the actual date and time of execution, delivery,
recordation, filing or perfection of any of the Senior Indebtedness, or the lien
or priority of payment thereof, and in any instance where the Senior
Indebtedness or any claim for the Senior Indebtedness is subordinated, avoided
or disallowed, in whole or in part, under Title 11 of the United States Code
(the "Bankruptcy Code") or other applicable federal or state law.

                            [SIGNATURE PAGE FOLLOWS]

                                       4

<PAGE>

            IN WITNESS WHEREOF, each of the parties hereto has caused a
counterpart of this Agreement to be duly executed and delivered as of the date
first above written.

                             BORROWER:

                             ITT CORPORATION,
                             a Nevada corporation

                             By:  /s/ Peter C. Morrow
                                 -----------------------------------------------
                                 Name: Peter C. Morrow
                                 Title: Vice President - Assistant Treasurer

                             LENDER:

                             SLT REALTY LIMITED PARTNERSHIP,
                             a Delaware limited partnership

                             By: Starwood Hotels & Resorts, a Maryland real
                                 estate investment trust, its general partner

                             By: /s/ Alan M. Schnaid
                                 -----------------------------------------------
                                 Name: Alan M. Schnaid
                                 Title: Vice President and Assistant Treasurer

                             STARWOOD HOTELS & RESORTS,
                             a Maryland real estate investment trust

                             By: /s/ Alan M. Schnaid
                                 -----------------------------------------------
                                 Name: Alan M. Schnaid
                                 Title: Vice President and Assistant Treasurer

                             STARWOOD HOTELS & RESORTS HOLDINGS, INC.,
                             an Arizona corporation

                             By:  /s/ David A. Hughes
                                  ----------------------------------------------
                                  Name: David A. Hughes
                                  Title: President

                                       5

<PAGE>

                                    EXHIBIT A

                               (Released Mortgage)

1.    Deed of Trust, Security Agreement and Financing Statement, dated as of
      February 23, 1998, by Sheraton Desert Inn Corporation, 357 Inc., Aronimink
      Corporation,

NEWYORK 169899V4:

      Baumgartner Company, Robert T. Knott, Jr., as Trustee of the TMA Trust
      dated July 1, 1996 and Robert T. Knott, Jr., as Trustee of the Levy Trust,
      and Charles W. Deaner, secured by property located at the Desert Inn, Las
      Vegas, Nevada.