<PAGE>   1
                                                                   EXHIBIT 10.15

        Amended New Era of Networks Change of Control Severance Agreement

The following represents the agreement between undersigned employee and New Era
of Networks, Inc. ("NEON") regarding the Change of Control Severance Agreement
dated 9/25/00 attached hereto (the "COC Agreement"), and any and all other terms
of employment that may exist between you and NEON.

1.   If a Change of Control (as defined below) is effected with Sybase, Inc. on
     or before June 21, 2001, you hereby release NEON (and its successors) from,
     and you hereby waive all terms, conditions and aspects of, the COC
     Agreement and any and all other employment arrangements that you have with
     NEON. "Change of Control" shall mean that Sybase, Inc. acquires a majority
     of the total voting power represented by NEON's then outstanding voting
     securities (i.e., Sybase, Inc. accepts under its tender offer at least a
     majority of the total voting power represented by NEON).

2.   In consideration of your waiving the COC Agreement, you will receive a cash
     payment of $1,560,000 (the "COC Payment") provided that you are employed
     by Sybase, Inc. or one of its subsidiaries at the time of the payment. 5/13
     on the 12th month anniversary, 3/13 on the 18th month anniversary and 5/13
     on the 24th month anniversary of the date that the Change of Control occurs
     (the "COC Event"). Notwithstanding the foregoing, if you are terminated by
     Sybase for any reason except for Cause (as defined below) prior to the
     second year anniversary of the COC Event, then (a) the balance of the COC
     Payment which has not been paid will be payable to you at the time of such
     termination, and (b) you shall be entitled for a period equal to the
     earlier of 24 months from the date of your termination or the date upon
     which you and your covered dependents become covered under comparable group
     health plans of another employer, to payment of applicable premiums under
     COBRA for group health coverage in order to provide you and your covered
     dependents equivalent coverage to which they were entitled to while you
     were an employee of Sybase, Inc. or any of its subsidiaries (together
     "Sybase").

          As used herein "Cause" shall mean:

          (i)   the continuous failure by you to perform the material duties and
                responsibilities that are reasonably consistent with your
                position which remain uncured for a period of fifteen (15) days
                after receipt of notice thereof from Sybase;

          (ii)  a conviction of, a plea of nolo contendere, a guilty plea or
                confession by you to a felony or the committing of an act of
                fraud or material dishonesty against, or the or embezzlement,
                theft or misappropriation of property belonging to, Sybase;

          (iii) you personally engaging in conduct that you reasonably should
                know or that you intend to be seriously injurious to the
                business of Sybase (it being understood that business decisions
                made by you in good faith are not to be considered grounds for
                termination for Cause); or


<PAGE>   2


          (iv)  the material breach by you of this Agreement or the
                Nondisclosure and Assignment of Inventions Agreement attached
                hereto which is not cured within fifteen (15) days after receipt
                of notice thereof from Sybase (except for a breach of the
                Nondisclosure and Assignment of Inventions Agreement for which
                no cure period is provided).

3.   As further consideration for this release and waiver, all stock options
     granted to you prior to the date of this Agreement will fully vest upon the
     COC Event. All restrictions on restricted stock granted or purchased prior
     to the date of this Agreement will lapse upon the COC Event.

4.   This Agreement will not be effective unless and until the COC Event occurs.
     If the COC Event does not occur prior to June 21, 2001, the COC Agreement
     shall remain in full force and effect.

5.   You are solely responsible for all Employee taxes in connection with any
     payments made to you under this Agreement.

6.   This Agreement contains the entire agreement between the parties with
     respect to the subject matter hereof and supercedes the COC Agreement in
     its entirety, that certain memorandum agreement dated 2/12/2001 between
     NEON and you, and all other employment arrangements that you have with
     NEON.

By accepting this release and waiver to the COC Agreement, you have freely and
voluntarily accepted its terms and conditions and have consulted with or had the
opportunity to consult advisors of your choice.

Accepted: /s/ PATRICK J. FORTUNE             NEON
          ------------------------
February 16, 2001                            By: /s/ LEONARD M. GOLDSTEIN
                                                 ---------------------------
                                                 Leonard M. Goldstein
                                                 Senior Counsel