<PAGE>

                                                                   EXHIBIT 10.15

THE RENCO GROUP, INC.
30 Rockefeller Plaza
New York, New York 10112

                                         November 15, 1999

Congress Financial Corporation,
  as Agent
1133 Avenue of the Americas
New York, New York 10036

              Re: Subordinated Loans in the Maximum Amount of $6,000,000
                  ------------------------------------------------------
Gentlemen:

         Lodestar Energy, Inc., a Delaware corporation ("Borrower"), has entered
into financing arrangements with Congress Financial Corporation, a Delaware
corporation in its capacity as Agent pursuant to the Loan Agreement (as
hereinafter defined) acting for and on behalf of the financial institutions
which are from time to time parties thereto as lenders (in such capacity,
"Agent"), The CIT Group/Business Credit, Inc. in its capacity as co-agent for
the financial institutions which are from time to time parties thereto as
lenders ("Co-Agent") and the financial institutions which are parties to the
Loan Agreement as lenders (individually, a "Lender", and collectively,
"Lenders") pursuant to which Agent and Lenders may make loans and advances and
provide other financial accommodations to Borrower as set forth in the Amended
and Restated Loan and Security Agreement, dated May 15, 1998, by and among
Borrower, Lodestar Holdings, Inc., a Delaware corporation ("Guarantor"), Agent,
Co-Agent and Lenders, as amended pursuant to Amendment No. 1 to Amended and
Restated Loan and Security Agreement, dated October 22, 1998, Amendment No. 2 to
Amended and Restated Loan and Security Agreement, dated December 21, 1998,
Amendment No. 3 to Amended and Restated Loan and Security Agreement, dated
January 15, 1999, Amendment No. 4 to Amended and Restated Loan and Security
Agreement, dated April 30, 1999, Amendment No. 5 to Amended and Restated Loan
and Security Agreement, dated July 16, 1999, and Amendment No. 6 to Amended and
Restated Loan and Security Agreement, dated of even date herewith (as the same
now exists or may hereafter be amended, modified, supplemented, extended,
renewed, restated or replaced, the "Loan Agreement"), and other agreements,
documents and instruments referred to therein or at any time executed and/or
delivered in connection therewith or related thereto, including, but not limited
to, this letter agreement (all of the foregoing, together with the Loan
Agreement, as the same now exist or may hereafter be amended, modified,
supplemented, extended, renewed, restated or replaced, being collectively
referred to herein as the "Financing Agreements"). All capitalized terms used
herein. unless otherwise defined herein, shall have the meanings given to such
terms in the Loan Agreement.

         In order to induce Agent and Lenders to enter into the financing
arrangements as provided in the Loan Agreement and the other Financing
Agreements and in consideration of the Loans and Letter of Credit Accommodations
to be provided by Agent and Lenders to Borrower pursuant thereto, the parties
hereto agree as follows:

         1. Subject to Section 5 below, at any time and from time to time within
ten (10) Business Days of any request of Agent (which request shall specify the
basis therefor under Section 5 below), Renco Group shall make loans to Borrower
in cash or other immediately available funds which loans shall be subordinated
loans in accordance with the Subordination Agreement, dated of even date
herewith, by and among Renco Group, Agent and Co-Agent (the "Renco Subordination
Agreement") in such amounts as Agent shall specify in any such request;
PROVIDED, THAT,

                  (a) the total amount of such subordinated loans by Renco
Group to Borrower shall not exceed $6,000,000 at any time outstanding,

                  (b) in the event that the basis for the request by Agent is
the condition set forth in Section 5(a), then the amount of such loans requested
by Agent may be up to: (i) the amount equal to the difference between $6,000,000
and the lowest amount of the Excess Revolving Credit Availability at any time
during the ten (10) day period referred to in Section 5(a), plus (ii)
$1,000,000,

                  (c) in the event that the basis for the request by Agent is
the condition set forth in Section 5(b) hereof, then the amount of such loans
requested by Agent may be up to $6,000,000,

                                       -1-

<PAGE>

                  (d) in the event that the basis for the request by Agent is an
Event of Default arising from the failure of Borrower to have Consolidated Net
Worth in an amount required under Section 7.10(b) of the Loan Agreement or the
failure to have cumulative EBITDA in the amount required under Section 7.25 of
the Loan Agreement, then the amount of such loans requested by Agent may be up
to: (i) the amount equal to the greater of: (A) the difference between the
amount of the Consolidated Net Worth which Borrower is required to have under
Section 7.10(b) of the Loan Agreement and the Consolidated Net Worth of Borrower
which is the basis for such Event of Default, or (B) the difference between the
cumulative EBITDA which Borrower is required to have under Section 7.25 of the
Loan Agreement and the cumulative EBITDA of Borrower which is the basis for such
Event of Default, PLUS (ii) $1,000,000,

                  (e) in the event that the basis for the request by Agent is
that any other Event of Default has occurred, then the amount of such loans
shall be equal to such amount (subject to clause (a) above) as Agent may
determine, and

                  (f) in the event that, at the time any such payment is
requested, Borrower is a debtor in any case under the U.S. Bankruptcy Code or
any similar proceeding under any state insolvency law, such payments by Renco
Group shall be made directly by Renco Group to Agent for the benefit of Lenders
to be applied to payment of the Obligations and shall not be deemed to
constitute a loan by Renco Group to Borrower (without limiting the rights of
Renco Group to reimbursement or subrogation subject to Section 6 hereof).

         2. Borrower and Renco Group each agree that the proceeds of any or all
such subordinated loans or other payments by Renco Group shall be used by
Borrower on the date of such payment by Renco Group to Borrower to make a
mandatory prepayment in respect of the Loans. Notwithstanding anything to the
contrary contained herein or in the other Financing Agreements, at any time on
or after an Event of Default, all amounts received by Agent pursuant hereto
shall be applied to the Obligations as specified by Section 4 below.

         3. (a) The Indebtedness of Borrower arising pursuant to the
subordinated loans by Renco Group to Borrower pursuant to the terms hereof shall
be subject to, and subordinate in right of payment to, the final payment and
satisfaction in full of all of the Obligations as set forth in the Renco
Subordination Agreement. As set forth therein, Borrower may make payments in
respect of the subordinated loans so long as the following conditions are
satisfied as reasonably determined by Agent: (i) as of the date of such payment
and after giving effect thereto, Excess Revolving Credit Availability shall be
not less than $12,000,000 and for each of the thirty (30) consecutive days
immediately prior to any such payment, Excess Revolving Credit Availability
shall not have been less than $12,000,000, and (ii) as of the date of any such
payment and after giving effect thereto, no Event of Default or act, condition
or event which with notice of passage of time or both would constitute an Event
of Default shall exist or have occurred and be continuing.

             (b) Borrower may, at any time, request that Agent agree to allow
payments to Renco Group in respect of the Indebtedness of Borrower to Renco
Group arising pursuant to such subordinated loans (other than as expressly
permitted in Section 3(a) above). Agent may, but shall not be obligated to agree
to allow such payments, subject to such terms and conditions as Agent may elect
to establish with respect thereto. The foregoing shall not be construed to
require Agent or Lenders to so agree and Agent and Lenders may withhold such
agreement in its and their discretion.

             (c) In the event that any amounts are repaid to Renco Group under
this Section 3, then the amount of the loans available for request by Agent
hereunder shall increase by the amount of any such repayment(s), subject to the
limitation in Section 1(a) hereof.

         4. Borrower hereby irrevocably authorizes and directs that Renco Group
make all such payments in respect of the subordinated loans provided for
hereunder directly to Agent for the ratable benefit of Lenders and for
application to the Obligations arising in connection with the Revolving Credit
Facility.

         5. The obligations of Renco Group to make the subordinated loans to
Borrower pursuant to Section 1 above shall be continuing from the date hereof
through and including the later of June 1, 2001 or the date that no Event of
Default, or act, condition or event which with notice or passage of time or both
would constitute an Event of Default shall exist or have occurred and be
continuing if such Event of Default or act, condition or event shall have first
occurred prior to June 1, 2001. Agent shall have the right to request such
subordinated loans and, upon such request, Renco Group shall make such
subordinated loans at any time and from time to time only if any of the
following occur: (a) the Excess Revolving Credit Availability shall be less than

                                      -2-
<PAGE>

$6,000,000 for any period of ten (10) consecutive Business Days, (b) at any time
there is no Excess Revolving Credit Availability, or (c) any Event of Default,
or act, condition or event which with notice or passage of time or both would
constitute an Event of Default shall exist or have occurred and be continuing.

         6. Except as otherwise provided herein and in the Renco Subordination
Agreement, Renco Group hereby irrevocably and unconditionally waives all
statutory, contractual, common law, equitable and other claims against Borrower,
or any of the Collateral for subrogation, reimbursement, exoneration,
contribution, indemnification or other recourse in respect of sums paid or
payable to Lenders by Renco Group hereunder until all of the Obligations are
paid and satisfied in full.

         7. Renco Group and Borrower represent and warrant to Agent and Lenders
that: (a) the execution, delivery and performance of this letter agreement is
within the corporate powers of Renco Group and Borrower, has been duly
authorized by all necessary corporate action of Renco Group and Borrower, and
does not contravene any law, any provisions of the certificate of incorporation
or the by-laws of Renco Group and Borrower or any agreement to which either of
Renco Group or Borrower is a party or by which it or its properties are bound,
and (b) this letter agreement constitutes the legal, valid and binding
obligations of Renco Group and Borrower, enforceable in accordance with its
terms.

         8. Notice of acceptance hereof, the making of Loans and providing
Letter of Credit Accommodations to, and the incurring of any expenses by or in
respect of, Borrower and Guarantor by Lender, and all other notices to which
Renco Group and Borrower are or may be entitled are hereby waived (except as to
Borrower as expressly provided for herein or in the Financing Agreements or the
Renco Subordination Agreement). Renco Group waives notice of, and hereby
consents to (a) any amendment, modification, supplement, renewal, restatement or
extensions of time of payment of or increase or decrease in the amount of any of
the Obligations or to the Loan Agreement or any of the other Financing
Agreements or any Collateral, (b) the taking, exchange, surrender and releasing
of Collateral or guarantees now or at any time held by or available to Lender
for the Obligations or any other person at any time liable for or in respect of
the Obligations, (c) the exercise of, or refraining from the exercise of any
rights against Borrower, Guarantor or any other obligor or any Collateral, (d)
the settlement, compromise or release of, or the waiver of any default with
respect to, any of the Lenders, and/or (e) any Obligations incurred, or grant of
a security interest to secure Obligations, under Section 364 of the U.S.
Bankruptcy Code to Borrower, as debtor-in-possession. Any of the foregoing shall
not, in any manner, affect the terms hereof or impair the obligations of Renco
Group hereunder. All of the Obligations shall be deemed to have been made or
incurred in reliance upon this letter agreement.

         9. This letter agreement shall be applicable both before and after the
filing of any petition by or against Borrower under the U.S. Bankruptcy Code and
all converted or succeeding cases in respect thereof, and all references herein
to Borrower shall be deemed to apply to a trustee for Borrower and Borrower as a
debtor-in-possession. The rights of Agent and Lenders and the obligations of
Renco Group hereunder shall continue after the filing thereof on the same basis
as prior to the date of the petition.

         10. The rights and obligations hereunder of each of the parties hereto
shall be governed by and interpreted and determined in accordance within the
laws of the State of New York (without giving effect to principles of conflict
of law).

         11. This letter agreement shall be binding upon and inure to the
benefit of each of the parties hereto and their respective successors and
assigns. All references to any party hereto shall be deemed to include such
party and its successors and assigns.

         12. This letter agreement may be executed in any number of
counterparts, but all of such counterparts shall together constitute but one and
the same agreement. Making proof of this agreement shall not be necessary to
produce or to account for more than one counterpart thereof signed by each of
the parties hereto.

         Upon the execution of this letter agreement by Agent, this letter shall
become a binding agreement by and among Renco Group, Borrower and Agent.

                                    Very truly yours,

                                    THE RENCO GROUP, INC.

                                    By:  /s/ Roger Fay
                                        ---------------

                                      -3-

<PAGE>
                                    Title:  /s/ Vice President
                                           --------------------

AGREED:
CONGRESS FINANCIAL CORPORATION,
as Agent

By: /s/ Thomas Martin
    ------------------
Title: /s/ Assistant Vice President
       ----------------------------

THE CIT GROUP/BUSINESS CREDIT, INC.,
as Co-Agent

By: /s/ Christopher Hill
    ---------------------
Title: /s/ Assistant Vice President
       -----------------------------
[SIGNATURES CONTINUED ON NEXT PAGE]


[SIGNATURES CONTINUED FROM PREVIOUS PAGE]


LODESTAR ENERGY, INC.

By: /s/ Roger Fay
    --------------
Title: /s/ Vice President
       -------------------

LODESTAR HOLDINGS, INC.

By: /s/ Roger Fay
    --------------
Title: /s/ Vice President
       -------------------


                                      -4-