Exhibit 10.15

Execution Version

COMMITMENT INCREASE AGREEMENT

March 3, 2020

JPMorgan Chase Bank, N.A., as Administrative

Agent for the Lenders party to the Credit

Agreement referred to below (the

“Administrative Agent”)

500 Stanton Christiana Road, NCC5/Floor 1

Newark, DE 19713

Ladies and Gentlemen:

We refer to the Amended and Restated Senior Secured Revolving Credit Agreement
dated as of November 7, 2019 (as amended, modified or supplemented from time to
time, the “Credit Agreement”; the terms defined therein being used herein as
therein defined) among FS KKR Capital Corp. (“FSK”) and FS KKR Capital Corp. II
(formerly known as FS Investment Corporation II and successor by merger to FS
Investment Corporation III) ( the “Relevant Borrower” and together with FSK, the
“Borrowers”), the Lenders party thereto, ING Capital LLC, as Collateral Agent,
and JPMorgan Chase Bank, N.A., as Administrative Agent for said Lenders. You
have advised us that the Relevant Borrower has requested in two letters, each
dated March 3, 2020 (the “Increase Requests”), from the Relevant Borrower to the
Administrative Agent that the aggregate amount of the Commitments be increased
on the terms and subject to the conditions set forth herein.

A. Commitment Increase. Pursuant to Section 2.07(e) of the Credit Agreement, BNP
Paribas and ING Capital LLC (each, an “Increasing Lender” and together the
“Increasing Lenders”), hereby severally agree to make Loans in the amount set
forth opposite the name of such Increasing Lender listed in Schedule I hereto
pursuant to the instruction of the Administrative Agent, such Loans to be
effective as of the Increase Date (as defined in the Increase Requests);
provided that (i) the Administrative Agent shall have received a duly executed
officer’s certificate from the Relevant Borrower, dated the Increase Date, in
substantially the form of Exhibit I and (ii) the Administrative Agent shall have
received evidence of the payment by the Relevant Borrower of all fees due and
payable to the Increasing Lenders on the Increase Date that the Relevant
Borrower has agreed to pay in connection with this Agreement.

B. Confirmation of Each Increasing Lender. Each Increasing Lender (i) confirms
that it has received a copy of the Credit Agreement and the other Loan
Documents, together with copies of the financial statements referred to therein
and such other documents and information as it has deemed appropriate to make
its own credit analysis and decision to enter into this Agreement; (ii) agrees
that it will, independently and without reliance upon the Administrative Agent
or any other Lender or Agent and based on such documents and information as it
shall deem appropriate at the time, continue to make its own credit decisions in
taking or not taking action under the Credit Agreement; and (iii) acknowledges
and agrees that, from and after the Increase Date and subject to the conditions
in Clause (A) above, the Commitment Increase set forth opposite the name of such
Increasing Lender listed in Schedule I hereto shall be included in the
Commitment, and the Commitment Increase shall be governed for all purposes by
the Credit Agreement and the other Loan Documents.

C. Counterparts, etc.. This Agreement may be executed in counterparts (and by
different parties hereto on different counterparts), each of which shall
constitute an original, but all of which when

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taken together shall constitute a single contract. Delivery of an executed
counterpart of a signature page to this Agreement by telecopy or e-mail shall be
effective as delivery of a manually executed counterpart of this Agreement. This
Agreement shall be deemed to be a Loan Document.

D. Governing Law, etc. The provisions of Sections 9.09 and 9.10 of the Credit
Agreement are incorporated herein by reference mutatis mutandis.

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Very truly yours, INCREASING LENDER BNP PARIBAS By:   /s/ Laurent Vanderzyppe
Name: Laurent Vanderzyppe Title: Managing Director By:   /s/ Liza Shabetayer
Name: Liza Shabetayer Title: Director

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INCREASING LENDER ING CAPITAL LLC By:   /s/ Patrick Frisch

Name: Patrick Frisch

Title: Managing Director

By:   /s/ Dominik Breuer

Name: Dominik Breuer

Title: Managing Director

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Accepted and agreed: FS KKR CAPITAL CORP. By:   /s/ William Goebel   Name:
William Goebel   Title: Chief Accounting Officer

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FS KKR CAPITAL CORP. II By:   /s/ William Goebel   Name: William Goebel   Title:
Chief Accounting Officer

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Acknowledged:

JPMORGAN CHASE BANK, N.A.,

as Administrative Agent

By:   /s/ Diego E. Nunes   Name: Diego E. Nunes   Title: Executive Director

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SCHEDULE I

 

Increasing Lender

   Multicurrency
Commitment  

BNP Paribas

   $ 70,000,000  

ING Capital LLC

   $ 20,000,000