<PAGE>   1
                                                                   EXHIBIT 10.15


                  AMENDMENT NO. 1 TO REVOLVING CREDIT AGREEMENT


         This Amendment No. 1 to Revolving Credit Agreement ("Amendment") dated
as of March 27, 2000 by and among the lenders signatories hereto ("Banks"),
Comerica Bank as agent for the Banks (in such capacity, "Agent"), and
Meadowbrook Insurance Group, Inc., a Michigan corporation ("Company").

                                    RECITALS

         A. Company and Banks entered into that certain Revolving Credit
Agreement dated as of August 3, 1999 ("Agreement").

         B. The parties desire to amend the Agreement.

         NOW, THEREFORE, the parties agree that the Agreement is amended as
follows:

         1. The definition of "Adjusted EBITDA" set forth in Section 1 of the
Agreement is amended to read in its entirety as follows:

                  "'Adjusted EBITDA' shall mean as of any date of determination,
         without duplication, the sum of (a) net income of Company, Meadowbrook,
         Inc., ASI, Inc., any Subsidiary which is not an Insurance Subsidiary or
         a Subsidiary regulated by any regulatory agency that regulates
         insurance companies and Crest Financial Corporation (excluding in the
         calculation thereof the net income of Williamsburg National Insurance
         Company) for the four preceding fiscal quarters ending on such date of
         determination, plus, to the extent deducted in determining net income,
         depreciation and amortization for such period, taxes on income for such
         period, Interest Expense for such period and, with respect to any
         determination of Adjusted EBITDA for any date of determination ending
         on or after December 31, 1999 and on or before December 31, 2000, any
         effect of any forgiveness of debt by Florida Preferred Administrators,
         Inc. to Southeastern Holdings Corporation, plus (b) an amount equal to
         fifty percent (50%) of the sum of net income of American Indemnity
         Insurance Company Ltd. for the four preceding fiscal quarters ending on
         such date of determination, plus, to the extent deducted in determining
         such net income, depreciation and amortization for such period, taxes
         on income for such period and Interest Expense for such period, plus,
         (c) one hundred percent (100%) of the amount available to be
         distributed by Star Insurance Company and any other Insurance
         Subsidiary not owned by Star Insurance Company to Company as of such
         date of determination, plus (e) dividends actually paid in cash by Star
         Insurance Company and any other Insurance Subsidiary not owned by Star
         Insurance Company to Company during such period."


<PAGE>   2



         2. The definition of "Net Worth" set forth in Section 1 of the
Agreement is amended to read in its entirety as follows:

                  "'Net Worth' shall mean, as of any applicable date of
         determination, the excess of (i) the book value of all assets of
         Company and its Consolidated Subsidiaries after all appropriate
         deductions in accordance with GAAP (including, without limitation,
         reserves for doubtful receivables, obsolescence, depreciation and
         amortization), over (ii) all Debt of Company and its Consolidated
         Subsidiaries, provided, however, in determining the book value of the
         assets of Company and its Consolidated Subsidiaries, the amount of any
         unrealized capital gains included in determining the book value of such
         assets shall be subtracted and the amount of any unrealized capital
         losses deducted in determining the book value of such assets shall be
         added back."

         3. The definition of "Base Net Worth" set forth in Section 1 of the
Agreement is amended to read in its entirety as follows:

                  "'Base Net Worth' shall mean (i) the amount determined from
         the following table, plus (ii) (on a cumulative basis) for each fiscal
         quarter ending after December 31, 2000, the sum of (A) seventy five
         percent (75%) of Net Income (if positive), earned in each fiscal
         quarter and (B) one hundred percent (100%) of the cash proceeds of the
         issuance of any Equity Interests of Company (net of reasonable and
         customary costs and expenses of issuance) during such fiscal quarter.

<TABLE>
<CAPTION>

         Period                                                           Amount
         ------                                                           ------
<S>                                                                   <C>
         March 31, 2000 through June 29, 2000                          $102,000,000
         June 30, 2000 through September 29, 2000                      $103,000,000
         September 30, 2000 through December 30, 2000                  $104,000,000
         December 31, 2000 and thereafter                              $106,000,000"
</TABLE>

         4. The following Section 2.10 is added to the Agreement:

                  "2.10 Reduction of Commitment. Upon receipt by Company of the
         net proceeds received in accordance with the provisions of Section
         7.20, the Revolving Credit Aggregate Commitment shall automatically
         decrease by the amount of such net proceeds, provided, however, the
         aggregate reduction shall not exceed $20,000,000. On the date of any
         such reduction, Company shall make any payments required pursuant to
         the provisions of Section 2.7.

         5. Section 4.1(c) of the Agreement is amended to read in its entirety
as follows and Schedule 1.1 to the Agreement is deleted and attached Schedule
1.1 is substituted in its place:



                                        2

<PAGE>   3



                  "(c) From the date hereof until the required date of delivery
         under Section 7.1(b) of the Company's financial statements for the
         fiscal quarter ending June 30, 2000, the margins and fee percentages
         shall be those set forth under the Level I column of the pricing matrix
         attached to this Agreement as Schedule 1.1."

         6. Section 7.9 of the Agreement is amended to read in its entirety as
follows:

                  "7.9 Maintain Base Net Worth. Beginning March 31, 2000,
         maintain at all times a Net Worth of not less than the Base Net Worth."

         7. Section 7.10 is amended to read in its entirety as follows:

                  "7.10 Fixed Charge Coverage Ratio. Maintain as of the end of
         each fiscal quarter, a Fixed Charge Coverage Ratio of not less than the
         following amounts during the periods specified below:

<TABLE>


<S>                                                                   <C>
         March 31, 2000 through June 29, 2000                          1.10 to 1.0
         June 30, 2000 through September 29, 2000                      1.00 to 1.0
         September 30, 2000 through December 30, 2000                  1.40 to 1.0
         December 31, 2000 through March 30, 2001                      1.65 to 1.0
         March 31, 2001 and thereafter                                 2.00 to 1.0"
</TABLE>

         8. The following Section 7.20 is added to the Agreement:

                  "7.20 Additional Capital. On or before June 30, 2000 obtain
         through the issuance of Equity Interests or the incurrence of
         Subordinated Debt on terms reasonably acceptable to the Majority Banks
         net proceeds to Company of not less than $10,000,000 and on or before
         September 30, 2000 obtain through the issuance of Equity Interests or
         the incurrence of Subordinated Debt net proceeds to Company of not less
         than an additional $10,000,000 and in each case apply to net proceeds
         to prepayment of the Advances."

         9. The following Section 7.21 is hereby added to the Agreement:

                  "7.21 Consultant. On or before April 15, 2000, engage an
         independent actuarial consultant acceptable to Agent to prepare an
         actuarial study of Star Insurance Company's loss reserves and provide
         to the Banks the final study on or before May 31, 2000."

         10. Section 8.4 of the Agreement is amended to read in its entirety as
follows:

                  "8.4 Acquisitions. Purchase or otherwise acquire or become
         obligated for the purchase of all or substantially all or any material
         portion of the assets or business



                                        3

<PAGE>   4



         interests of any Person, firm or corporation, or any shares of stock
         (or other ownership interests) of any corporation, trusteeship or
         association, or any business or going concern, or in any other manner
         effectuate or attempt to effectuate an expansion of present business by
         acquisition, except for Permitted Acquisitions, provided, however, no
         Permitted Acquisition may be consummated unless at the time of such
         acquisition and after giving effect thereto the Fixed Charge Coverage
         Ratio is greater than 2.0 to 1.0 and the ratio of Funded Debt to Total
         Capitalization has been less than .35 to 1.0 for the three consecutive
         fiscal quarters immediately preceding such acquisition."

         11. Section 8.6(b) is amended to add the following in the first line
after the words "Event of Default":

                  "(including, without limitation, any Default or Event of
         Default with respect to the provisions of Section 7.10)"

         12. Company violated the provisions of Sections 7.9 and 7.10 for the
period ended December 31, 1999. The Banks waive such violations of such
covenants for the period ended December 31, 1999. This waiver shall not act as a
consent or waiver of any other transaction, act or omission, whether related or
unrelated thereto, including any noncompliance with such covenant for any period
other than the period ending December 31, 1999. This waiver shall not extend to
or affect any obligation, covenant, agreement or default not expressly waived
hereby.

         13. Company hereby represents and warrants that, after giving effect to
the amendments contained herein, (a) execution, delivery and performance of this
Amendment and any other documents and instruments required under this Amendment
or the Agreement are within Company's powers, have been duly authorized, are not
in contravention of law or the terms of the Company's Articles of Incorporation
or Bylaws and do not require the consent or approval of any governmental body,
agency, or authority; and this Amendment and any other documents and instruments
required under this Amendment or the Agreement, will be valid and binding in
accordance with their terms; (b) the representations and warranties of Company
set forth in Sections 6.1 through 6.19 of the Agreement are true and correct in
all material respects on and as of the date hereof with the same force and
effect as if made on and as of the date hereof; (c) the representations and
warranties of Company set forth in Section 6.20 of the Agreement are true and
correct in all material respects as of the date hereof with respect to the most
recent financial statements furnished to the Bank by Company in accordance with
Section 7.1 of the Agreement; and (d) no Event of Default, or condition or event
which, with the giving of notice or the running of time, or both, would
constitute an Event of Default under the Agreement, has occurred and is
continuing as of the date hereof.

         14. This Amendment shall be effective upon (a) execution hereof by
Company, Agent and the Majority Banks, (b) payment by Company to Bank of an
amendment fee in the amount of $150,000, which fee shall be non-refundable and
shall be deemed fully earned upon execution of this Agreement, and (c) execution
by the Guarantors of the attached Acknowledgment.

                                        4

<PAGE>   5



         15. This Amendment may be signed in any number of counterparts, each of
which when so executed and delivered shall be deemed an original, but all such
counterparts together shall constitute but one and the same instrument.

                  WITNESS the due execution hereof as of the day and year first
above written.


COMERICA BANK, as Agent                         MEADOWBROOK INSURANCE
                                                GROUP, INC.



By: /s/ Jon E. Sasinowski                       By: /s/ W.J. Lohmeyer
   --------------------------                      -----------------------------
   Jon E. Sasinowski                               W.J. Lohmeyer

Its: Vice President                             Its: Sr. Vice President & C.F.O.
                                                    ----------------------------


BANKS:                                          COMERICA BANK



                                                By: /s/ Jon E. Sasinowski
                                                   -----------------------------
                                                   Jon E. Sasinowski

                                                Its: Vice President


                                                BANK ONE



                                                By: /s/ Jacqueline P. Yardley
                                                   -----------------------------
                                                   Jacqueline P. Yardley

                                                Its: First Vice President
                                                    ----------------------------





                                        5

<PAGE>   6



                                 ACKNOWLEDGMENT



         The undersigned Guarantors acknowledge the foregoing Amendment No. 1 to
Credit Agreement and further acknowledged that the Guaranty dated August 3, 1999
from the Guarantors in favor of the Agent and the Banks remains in full force
and effect in accordance with its terms.

                                          MEADOWBROOK, INC., a Michigan
                                          corporation



                                          By: /s/ Robert S. Cubbin
                                             ------------------------------
                                             Robert S. Cubbin

                                          Its: President
                                              -----------------------------


                                          MEADOWBROOK OF FLORIDA, INC.,
                                          a Florida corporation



                                          By: /s/ Robert S. Cubbin
                                             ------------------------------
                                             Robert S. Cubbin

                                          Its: Executive Vice President
                                              -----------------------------


                                          ASSOCIATION SELF INSURANCE
                                          SERVICES, INC., an Alabama corporation



                                          By: /s/ Robert S. Cubbin
                                             -------------------------------
                                             Robert S. Cubbin

                                          Its: Director & Secretary
                                              ------------------------------






                                        6

<PAGE>   7



                                         CREST FINANCIAL CORPORATION, a
                                         Nevada corporation



                                         By: /s/ Robert S. Cubbin
                                            --------------------------------
                                            Robert S. Cubbin

                                         Its: Chairman of the Board
                                             -------------------------------



                                        7

<PAGE>   8


                                  SCHEDULE 1.1

                               APPLICABLE MARGINS


<TABLE>
<CAPTION>

     BASIS FOR PRICING        LEVEL I          LEVEL II          LEVEL III         LEVEL IV          LEVEL V
---------------------------------------------------------------------------------------------------------------
<S>                         <C>           <C>               <C>               <C>                <C>
Fixed Charge                 <1.10         >1.10 to 1.0      >1.50 to 1.0       >2.0 to 1.0        >2.5 to 1.0
Coverage Ratio                                  and               and               and                and
(and with respect to                       <1.50 to 1.0      <2.0 to 1.0        <2.5 to 1          Funded Debt
Levels IV and V,                                                                    and           to Total Cap
Funded Debt to                                                                  Funded Debt to      <.15 to 1
Total                                                                              Total
Capitalization)                                                                Capitalization
                                                                                <.35 to 1.0
---------------------------------------------------------------------------------------------------------------
Prime-based                     1%               .75%             .50%              .25%                0%
Margin
---------------------------------------------------------------------------------------------------------------
Eurocurrency                   2.50%             2.25%            2.00%             1.65%              1.25%
Margin
---------------------------------------------------------------------------------------------------------------
Letter of Credit Fee           2.50%             2.25%            2.00%             1.65%              1.25%
---------------------------------------------------------------------------------------------------------------
</TABLE>





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