<PAGE>
                                                                   EXHIBIT 10.15
 
                             COOPERATION AGREEMENT
 
    This Agreement is made and entered into as of March 4, 1998, by and between
Universal International, Inc., a Minnesota corporation ("UNIVERSAL") and 99CENTS
Only Stores, a California corporation ("99CENTS ONLY") with respect to the
following:
 
                                R E C I T A L S
 
    WHEREAS, on November 17, 1997, 99CENTS Only acquired 4,500,000 shares of the
common stock, $0.001 par value per share (the "Common Stock"), of Universal,
representing approximately 48% of the outstanding Common Stock;
 
    WHEREAS, on February 17, 1998, 99CENTS Only publicly announced that it had
made a proposal to the Board of Directors of Universal to acquire 100% of the
outstanding Common Stock of Universal for an exchange ratio of one share of
99CENTS Only for each 16 shares of Universal Common Stock;
 
    WHEREAS, 99CENTS Only has determined to effect the acquisition by an
exchange offer (the "Offer") to all of the Universal stockholders;
 
                               A G R E E M E N T
 
    NOW, THEREFORE, in consideration of the foregoing and of the
representations, warranties, covenants and agreements contained herein, the
parties to this Agreement hereby agree as follows:
 
    1.  AGREEMENT TO SUPPORT TENDER OFFER GENERALLY.  Universal agrees to
support the Offer by 99CENTS Only and not to make any statement privately or
publicly opposing the Offer. Universal hereby agrees to cooperate generally with
99CENTS Only in the Offer by providing access during normal business hours to
the books and records of Universal, as well as to Universal's officers and
directors for purposes of providing information to make all appropriate filings
under the applicable federal and state laws. Furthermore, Universal agrees to
assist 99CENTS Only in soliciting proxies in favor of affording voting rights to
the shares of Universal acquired by 99CENTS Only in the Offer.
 
    2.  SCHEDULE 14D-9.  Universal hereby agrees to file with the Securities and
Exchange Commission ("SEC") in accordance with the provisions of the Securities
Exchange Act of 1934, as amended (the "Exchange Act"), its Solicitation
Recommendation Statement on Schedule 14D-9 pertaining to the Offer (together
with any amendments or supplements thereto, the "Schedule 14D-9") and to mail
promptly (but in no event later than as is required by applicable law) the
Schedule 14D-9 to the stockholders of Universal. Universal agrees that in the
Schedule 14D-9 it will not oppose the Offer and will either support the Offer or
take a position neutral to the position of 99CENTS Only. Universal shall provide
to 99CENTS Only and its counsel draft copies of the Schedule 14D-9 as soon as
practicable prior to its filing with the SEC such that 99CENTS Only and its
legal counsel shall have a reasonable opportunity to review and comment on the
Schedule 14D-9. Universal shall provide to 99CENTS Only and its counsel in
writing any comments Universal or its counsel may receive from the SEC or its
staff with respect to the Schedule 14D-9 as soon as practicable after the
receipt thereof. Universal represents and warrants to 99CENTS Only that the
Schedule 14D-9 will comply in all material respects with the provisions of
applicable federal securities laws and the securities laws of the State of
Minnesota. Each of 99CENTS Only and Universal represents and warrants to the
other that the information provided and to be provided by 99CENTS Only and
Universal, as the case may be, by or through their respective representatives
for use in the Schedule 14D-9 shall not, on the date filed with the SEC, on the
dates first published or sent or given to the stockholders of Universal and on
the expiration date of the Offer, contain any untrue statement of a material
fact with respect to such party or omit to state any material fact with respect
to such party required to be stated therein or necessary in order to make the
statements therein, in light of the circumstances under which they were made,
not misleading. Universal and 99CENTS Only each agrees to correct promptly any
information provided by it for use in the Schedule 14D-9 if and to the extent
that it shall have become false or misleading in any material respect, and
Universal further agrees to take all steps
<PAGE>
necessary to cause the Schedule 14D-9 as so corrected to be filed with the SEC
and to be disseminated to stockholders of Universal to the extent required by
applicable federal securities laws and the Minnesota Business Corporation Act
("Minnesota Laws").
 
    3.  STOCKHOLDER LISTS.  In connection with the Offer, Universal will
promptly furnish 99CENTS Only with mailing labels, security position listings
and any available listing or computer file containing the names and addresses of
the record holders of Universal Common Stock as of a recent date and shall
furnish 99CENTS Only with such additional information and assistance as 99CENTS
Only or its agents may reasonably request in communicating the Offer to the
record and beneficial holders of Universal Common Stock. Subject to the
requirements of applicable law, and except for such steps as are necessary to
disseminate the Offer documents, 99CENTS Only and their affiliates, associates,
agents and advisors shall use the information contained in any such labels,
listing and files only in connection with the Offer and, if this Agreement shall
be terminated, will deliver to Universal all copies of such information then in
their possession.
 
    4.  COMPOSITION OF THE BOARD OF DIRECTORS; SECTION 14(f).  (a) In the event
that immediately following the Offer, 99CENTS Only owns at least a majority of
the Universal Common Stock outstanding, 99CENTS Only shall be entitled to
designate for appointment or election to Universal's Board of Directors and any
committee thereof, upon written notice to Universal, that number of directors
equal to the product of (i) the number of directors on the Universal Board of
Directors or the applicable committee and (ii) the percentage which the number
of shares of Universal Common Stock held by 99CENTS Only after the Offer bears
to the total number of shares of Universal Common Stock outstanding, rounded up
to the next whole number. Prior to consummation of the Offer, the Board of
Directors of Universal will use its best efforts to either adopt an amendment to
Universal's By-Laws to provide in effect that upon the request of 99CENTS Only
following the acquisition by 99CENTS Only of a majority of the shares of
Universal Common Stock outstanding pursuant to the Offer, the number of members
of Universal's Board of Directors and any committee thereof shall be increased
to the extent necessary to provide the persons designated by 99CENTS Only
pursuant to this Section with representation on the Board of Directors and its
committees, or will obtain the resignation of such number of directors as is
necessary to enable such number of 99CENTS Only designees to be so elected.
 
    (b) Universal's obligations to cause designees of 99CENTS Only to be elected
or appointed to the Board of Directors of Universal and any committee thereof
shall be subject to Section 14(f) of the Exchange Act and Rule 14f-1 promulgated
thereunder. Universal shall promptly take all actions required pursuant to such
Section and Rule in order to fulfill its obligations under this Section and
shall include in the Schedule 14D-9 such information with respect to 99CENTS
Only and its officers and directors as is required under such Section and Rule
in order to fulfill its obligations under this Section. 99CENTS Only will supply
to Universal in writing any information with respect to it and its nominees,
officers, directors and affiliates required by such Section and Rule.
 
    5.  APPROVAL OF THE STOCKHOLDERS.  Pursuant to the requirements of Section
302A.671 of the Minnesota Laws, the Offer requires (i) the affirmative vote of
the holders of a majority of the voting power of all shares of Common Stock of
Universal entitled to vote, including all shares held by 99CENTS Only, and (ii)
the affirmative vote of the holders of a majority of the voting power of all
shares of Common Stock of Universal entitled to vote, excluding the shares held
by 99CENTS Only, and shares held by officers and employee directors of
Universal. Without the affirmative vote of the stockholders of Universal, the
shares of Universal Common Stock acquired by 99CENTS Only representing over 50%
of the outstanding Common Stock of Universal would be denied voting rights. In
accordance with Section 302A.671, 99CENTS Only and Universal shall cooperate to
prepare and file with the SEC a registration statement on Form S-4 (the
"Registration Statement"), a portion of which shall include a proxy statement
(the "Offer Proxy Statement/Prospectus") with respect to a meeting of
stockholders of Universal to vote on the Offer for purposes of Section 302A.671
of the Minnesota Laws. Each of 99CENTS Only and Universal represents and
warrants to the other that the information provided and to be provided by
99CENTS Only and Universal, as the case may be, by or through their respective
representatives for use in the Registration Statement shall not, and on the date
filed with the SEC, and with respect to the Offer Proxy Statement/ Prospectus,
on the dates first published or sent or given to the holders of Universal Common
Stock,
<PAGE>
contain any untrue statement of a material fact with respect to such party or
omit to state any material fact with respect to such party required to be stated
therein or necessary in order to make the statements therein, in light of the
circumstances under which they were made, not misleading. Universal and 99CENTS
Only each agrees to correct promptly any information provided by it for use in
the Offer Proxy Statement/Prospectus if and to the extent that it shall have
become false or misleading in any material respect, and 99CENTS Only further
agrees to take all steps necessary to cause the Registration Statement as so
corrected to be filed with the SEC and for the Offer Proxy Statement/Prospectus
to be disseminated to the holders of shares of Universal Common Stock, in each
case as and to the extent required by applicable federal securities laws and the
Minnesota Laws. Universal agrees to use its best efforts to obtain the approval
of its stockholders pursuant to Section 302A.671 of the Minnesota Laws.
 
    6.  TAKEOVER PROVISIONS INAPPLICABLE; AMENDMENT TO RIGHTS
AGREEMENT.  Universal agrees to take all necessary action to approve an
amendment of the Rights Agreement, dated as of April 19, 1996 (the "Rights
Agreement"), between Universal and Norwest Bank Minnesota, N.A., as rights agent
Rights Agreement so that (a) none of the execution or delivery of this
Agreement, the making of the Offer, the acceptance for payment or payment for
shares of Universal Common Stock by 99CENTS Only pursuant to the Offer or the
consummation of any other transaction with 99CENTS Only will result in (i) the
occurrence of the "Distribution Date" described under Section 3 of the Rights
Agreement, or (ii) the common stock purchase rights (the "Company Rights")
issued pursuant to the Rights Agreement becoming evidenced by, and transferable
pursuant to, certificates separate from the certificates representing Universal
Common Stock, or (b) the Company Rights will be redeemed prior to 99CENTS Only
becoming an "Acquiring Person" pursuant to the terms of the Rights Agreement.
 
    7.  FILINGS.  99CENTS Only and Universal agree to (a) use all reasonable
efforts to cooperate with one another in (i) determining which filings are
required to be made prior to consummation of the Offer, and which consents,
approvals, permits or authorizations are required to be obtained from states and
foreign jurisdictions in connection with the consummation of the Offer and (ii)
timely making such filings and timely seeking all such consents, approvals,
permits or authorizations; and (b) use all reasonable efforts to take, or cause
to be taken, all other action and do, or cause to be done, all other things
necessary, proper or appropriate to consummate and make effective the Offer.
 
    8.  TERMINATION.  This Agreement may be terminated (i) by either 99CENTS
Only or Universal if the Offer shall not have been consummated on or before
September 30, 1998 or (ii) by the mutual written consent of Universal and
99CENTS Only authorized by their respective Boards of Directors. If this
Agreement is terminated pursuant to this Section, this Agreement shall become
void and of no effect with no liability on the part of any party hereto.
 
    9.  MISCELLANEOUS.
 
        (a)  SEVERABILITY.  Should any Section or any part of a Section within
    this Agreement be rendered void, invalid or unenforceable by any court of
    law for any reason, such invalidity or unenforceability shall not void or
    render invalid or unenforceable any other Section or part of a Section in
    this Agreement.
 
        (b)  GOVERNING LAW.  Except to the extent that the laws of Minnesota are
    mandatorily applicable to the Offer, this Agreement shall be governed by,
    and construed in accordance with, the laws of the State of California
    applicable to contracts executed in and to be performed in that State. All
    actions and proceedings arising out of or relating to this Agreement shall
    be heard and determined in any U.S. federal court located in the City of Los
    Angeles. The parties hereto hereby (i) submit to the exclusive jurisdiction
    of any U.S. federal court located in the City of Los Angeles for the purpose
    of any action arising out of or based upon this Agreement or the Offer
    brought by any party hereto, and (ii) waive, and agree not to assert by way
    of motion, as a defense, or otherwise, in any such action, any claim that it
    is not subject personally to the jurisdiction of the above-named courts,
    that its property is exempt or immune from attachment or execution, that the
    action is brought in an inconvenient forum, that the venue of the action is
    improper, or that this Agreement or the Offer may not be enforced in any or
    by any of the above-named courts.
<PAGE>
        (c)  NO ADVERSE CONSTRUCTION.  The rule that a contract is to be
    construed against the party drafting the contract is hereby waived, and
    shall have no applicability in construing this Agreement or any provisions
    hereof.
 
        (d)  COUNTERPARTS.  This Agreement may be executed in one or more
    counterparts, each of which shall be deemed an original but all of which
    together shall constitute one and the same instrument.
 
        (e)  COSTS AND ATTORNEYS' FEES.  In the event that any action, suit, or
    other proceeding is instituted concerning or arising out of this Agreement,
    the prevailing party shall recover all of such party's costs, and reasonable
    attorneys' fees incurred in each and every such action, suit, or other
    proceeding, including any and all appeals or petitions therefrom.
 
        (f)  SUCCESSORS AND ASSIGNS.  All rights, covenants and agreements of
    the parties contained in this Agreement shall, except as otherwise provided
    herein, be binding upon and inure to the benefit of their respective
    successors and assigns.
 
        (g)  AMENDMENT.  This Agreement may be amended by the parties hereto, by
    action taken by their respective Boards of Directors at any time before or
    after approval hereof by the stockholders, but after any such approval, no
    amendment shall be made which changes the consideration to be paid to the
    stockholders pursuant to the Offer, or which is otherwise not permitted by
    the California or Minnesota Laws, without the further approval of the
    stockholders. This Agreement may not be amended except by an instrument in
    writing signed on behalf of each of the parties hereto.
 
        (h)  BEST EFFORTS.  Subject to the terms and conditions of this
    Agreement, each party will use its best efforts to take, or cause to be
    taken, all actions and do, or cause to be done, all things necessary, proper
    or advisable under applicable laws and regulations to consummate the
    transactions contemplated by this Agreement.
 
    IN WITNESS WHEREOF, the parties hereto have executed and delivered this
Agreement as of the date first above written.
 
<TABLE>
<S>                             <C>  <C>
                                99CENTS ONLY STORES
                                A CALIFORNIA CORPORATION
 
                                By:  /s/ DAVID GOLD
                                     -----------------------------------------
                                     Name: David Gold
                                     Title: President and Chief Executive
                                     Officer
 
                                UNIVERSAL INTERNATIONAL, INC.
                                A MINNESOTA CORPORATION
 
                                By:  /s/ RICHARD ENNEN
                                     -----------------------------------------
                                     Name: Richard Ennen
                                     Title: President and Chief Executive
                                     Officer
</TABLE>