<PAGE>   1
                                                                   EXHIBIT 10.15

                       AMENDMENT TO MANAGEMENT AGREEMENT

         This Amendment to Management Agreement is executed this 30th day of
November 1999 by and between Ingalls Provider Group (the "COMPANY") and North
American Medical Management -- Illinois, Inc.("NAMM").

         WHEREAS, the Company and NAMM entered into a certain Management
Agreement (the "Agreement") dated March 14, 1994; and

         WHEREAS, NAMM and Northwestern Healthcare Network ("NHN") entered into
that certain Master Agreement dated June 29, 1994 (the "Master Agreement"); and

         WHEREAS, the Company is affiliated with a hospital member (the
"Hospital") of NHN; and

         WHEREAS, NHN and its members have decided to dissolve NHN effective
December 31, 1999 and thus to terminate the Master Agreement, at which time
Company and Hospital shall no longer be affiliated with NHN; and

         WHEREAS, Section 7.02(G) of the Agreement provides for the termination
of the Agreement if Hospital at any time ceases to be affiliated with NHN; and

         WHEREAS, the Company and NAMM mutually desire to amend the Agreement to
provide for the continuation of the Agreement, upon the terms and conditions set
forth herein.

         NOW, THEREFORE, for and in consideration of the premises and the mutual
covenants and promises contained herein, the receipt and sufficiency of which is
hereby acknowledged, the parties hereto agree as follows:

         1.       The dissolution of NHN and the termination of the Master
                  Agreement shall not cause the termination of the Agreement.
                  Section 7.02(G) of the Agreement is hereby deleted.

         2.       Section 7.01 "Term" of the Agreement is deleted and in its
                  place the following is substituted:

                  7.01         Term
                               The term of this Agreement shall be from the
                               Effective Date (March 1, 1995) and shall
                               continue for a period of seven (7) years.

         3.       Section 5.02 "NAMM's Participation in any Company Profits" and
                  Section 5.04 "Payment of Expense Reimbursements to NAMM" are
                  deleted and in their place are substituted:


<PAGE>   2

                  5.02     Management Fee and Surplus Sharing
                           From July 1, 1999 until December 31, 2000 NAMM shall
                           receive $4.50 per Commercial or Medicaid enrollee per
                           month plus 20% of the profits of the Company.

                           From January 1, 2001 until February 28, 2002 NAMM
                           shall receive $4.75 per Commercial or Medicaid
                           enrollee per month plus 20% of the profits of the
                           Company.

                           From the July 1, 1999 until February 28, 2002 NAMM
                           shall receive $20.50 per Medicare enrollee per month
                           plus 20% of the profits of the Company.

                           Any NAMM management services for provider-sponsored,
                           self-insured, or global-risk products will be
                           negotiated separately from this Amendment.

         4.       The terms and conditions of the Master Agreement and that
                  certain Joint Marketing Strategy (the "Joint Marketing
                  Strategy") document executed by NHN and NAMM shall no longer
                  have any effect on the terms and conditions of the Agreement
                  or the parties' responsibilities and/or rights thereunder. All
                  provisions of the Agreement relating to or referencing the
                  Master Agreement and the Joint Marketing Strategy are hereby
                  agreed to be null and void and to have no effect, and
                  specifically Section 1.02 "Master Agreement" and Section 6.01
                  "Joint Market Strategy" are hereby deleted from the Agreement.
                  Section 6.03 "NAMM Exclusivity" is deleted and replaced with
                  the following:

                  6.03     NAMM Exclusivity. NAMM will not, during the term of
                           this Agreement, provide any services similar to the
                           services being provided to the Company to any
                           hospital or Physician Hospital Organization within
                           fifteen miles of the Hospital, unless agreed to by
                           the Company.

         5.       Company will pay NAMM the sum of Eighty Thousand and No/100
                  Dollars ($80,000.00) as specific consideration for management
                  cost overruns incurred by NAMM from the Effective Date of the
                  Agreement through the Amendment Date.

         6.       In all other respects, the terms and conditions of the
                  Agreement remain unchanged.

<PAGE>   3

         IN WITNESS WHEREOF, the parties hereto have caused their duly appointed
representatives to execute this Amendment to Management Agreement as of the day
and date written above.

INGALLS PROVIDER GROUP




By: /s/
    -------------------------------------

Its: President

NORTH AMERICAN MEDICAL MANAGEMENT -- ILLINOIS, INC.




By: /s/
    ------------------------------------

Its: Regional Vice President
     ------------------------------------