<PAGE>

                                                          Exhibit 10.15

                     SEVENTH LEASE AMENDMENT
                     -----------------------

Agreement   made   this  28th  day  of  October,  1996   by   and   between
Rosewood  III  Associates,  L.P.,  with  mailing  address  at  293   Boston
Post    Road   West,   Suite   320,   Marlborough,   Massachusetts,   01752
(hereinafter   referred   to   as  "Landlord")   and   Viewlogic   Systems,
Inc.,  with  a  principal  place  of  business  at  293  Boston  Post  Road
West,   Marlborough,   Massachusetts,  01752,  (hereinafter   referred   to
as "Tenant").

WHEREAS,   Landlord  and  Tenant  have  entered  into   a   certain   lease
dated   November  16,  1989  and  subsequent  Amendments  dated  June   15,
1990,   August   22,   1991,  October  30,  1991,   September   17,   1993,
February   7,  1995,  February  12,  1996  (hereinafter  referred   to   as
the  "Lease")  relating  to  a  certain  space  at  293  Boston  Post  Road
West, Marlborough, Massachusetts, 01752.

WHEREAS,  Landlord  and  Tenant  have  agreed  to  modify  and  amend   the
Lease   by  modifying  the  Annual  Fixed  Rent  and  to  make  such  other
modifications   and   amendments  to  the  Lease  as  may   be   necessary,
all   as  more  fully  set  forth  hereinbelow,  which  modifications   and
amendments shall be effective as of November 1, 1996.

NOW   THEREFORE,   for   good  and  valuable  consideration   the   receipt
and   sufficiency   of   which   is  hereby  acknowledged,   Landlord   and
Tenant hereby agree as follows:

Section   1.01   of  said  Article  1  is  hereby  further   modified   and
amended   by   deleting  therefrom  the  dates  "February   12,   1990   to
February   28,   2000"  set  forth  in  the  subsection  thereof   entitled
(Term)   and  by  substituting  therefor  the  dates  "February  12,   1990
to October 31, 2002".

Landlord   and   Tenant   hereby   agree   that   except   as   hereinabove
specifically   modified  and  amended,  the  Lease  is  and  shall   remain
in   full   force   and   effect  in  accordance   with   the   terms   and
provisions set forth in the Lease.

IN   WITNESS   WHEREOF.  Landlord  and  Tenant  have  duly   executed   the
Seventh  Lease  Amendment  under  seal as  of  the  30th  day  of  October,
1996.


LANDLORD:                                  TENANT:
Rosewood III Associates, L.P.              Viewlogic Systems, Inc

/s/ Robert J. Depietri, Jr.                /s/  David Adey
---------------------------                ------------------
Robert J. Depietri, Jr.                    David Adey

Its:  General Partner                      Its:  Vice President of Human
                                                 Resources
                                  19
<PAGE>

                            VIEWLOGIC
                         RENT SCHEDULE A
<TABLE>
<CAPTION>
                                                               
                OFFICE    OFFICE             STORAGE   STORAGE          
                ANNUAL    TOTAL              ANNUAL     TOTAL       TOTAL
 DATE           FIXED    MONTHLY              FIXED    MONTHLY     MONTHLY
 RENT   OFFICE  RENT      FIXED     STORAGE    RENT     FIXED       FIXED
  DUE     SF    P.S.F.     RENT       SF      P.S.F.     RENT        RENT
-----   ------  ------   --------   -------  -------   -------     -------
<C>     <C>     <C>     <C>           <C>     <C>     <C>         <C>
1/1/96  92,340  $16.00  $123,120.00   6,414   $5.00   $2,672.50   $125,792.50
2/1/96  92,340   16.00   123,120.00   6,414    5.00    2,672.50    125,792.50
3/1/96  92,340   16.00   123,120.00   6,414    5.00    2,672.50    125,792.50
4/1/96  92,340   16.00   123,120.00   6,414    5.00    2,672.50    125,792.50
5/1/96  92,340   16.00   123,120.00   6,414    5.00    2,672.50    125,792.50
6/1/96  92,340   16.00   123,120.00   6,414    5.00    2,672.50    125,792.50
7/1/96  92,340   16.00   123,120.00   6,414    5.00    2,672.50    125,792.50
8/1/96  92,340   16.00   123,120.00   6,414    5.00    2,672.50    125,792.50
9/1/96  92,340   16.00   123,120.00   6,414    5.00    2,672.50    125,792.50
10/1/96 92,340   16.00   123,120.00   6,414    5.00    2,672.50    125,792.50
-----------------------------------------------------------------------------
11/1/96 95,220   16.00   126,960.00   6,414    5.00    2,672.50    129,632.50
12/1/96 95,220   16.00   126,960.00   6,414    5.00    2,672.50    129,632.50
1/1/97  95,220   16.00   126,960.00   6,414    5.00    2,672.50    129,632.50
2/1/97  95,220   16.00   126,960.00   6,414    5.00    2,672.50    129,632.50
3/1/97  95,220   16.00   126,960.00   6,414    5.00    2,672.50    129,632.50
4/1/97  95,220   16.00   126,960.00   6,414    5.00    2,672.50    129,632.50
5/1/97  95,220   16.00   126,960.00   6,414    5.00    2,672.50    129,632.50
6/1/97  95,220   16.00   126,960.00   6,414    5.00    2,672.50    129,632.50
7/1/97  95,220   16.00   126,960.00   6,414    5.00    2,672.50    129,632.50
8/1/97  95,220   16.00   126,960.00   6,414    5.00    2,672.50    129,632.50
9/1/97  95,220   16.00   126,960.00   6,414    5.00    2,672.50    129,632.50
10/1/97 95,220   16.00   126,960.00   6,414    5.00    2,672.50    129,632.50
11/1/97 95,220   16.00   126,960.00   6,414    5.00    2,672.50    129,632.50
12/1/97 95,220   16.00   126,960.00   6,414    5.00    2,672.50    129,632.50
1/1/98  95,220   16.00   126,960.00   6,414    5.00    2,672.50    129,632.50
2/1/98  95,220   16.00   126,960.00   6,414    5.00    2,672.50    129,632.50
3/1/98  95,220   16.00   126,960.00   6,414    5.00    2,672.50    129,632.50
-----------------------------------------------------------------------------
4/1/98  95,220   16.25   128,943.75   6,414    5.00    2,672.50    131,616.25
5/1/98  95,220   16.25   128,943.75   6,414    5.00    2,672.50    131,616.25
6/1/98  95,220   16.25   128,943.75   6,414    5.00    2,672.50    131,616.25
7/1/98  95,220   16.25   128,943.75   6,414    5.00    2,672.50    131,616.25
8/1/98  95,220   16.25   128,943.75   6,414    5.00    2,672.50    131,616.25
9/1/98  95,220   16.25   128,943.75   6,414    5.00    2,672.50    131,616.25
10/1/98 95,220   16.25   128,943.75   6,414    5.00    2,672.50    131,616.25
11/1/98 95,220   16.25   128,943.75   6,414    5.00    2,672.50    131,616.25
12/1/98 95,220   16.25   128,943.75   6,414    5.00    2,672.50    131,616.25
1/1/99  95,220   16.25   128,943.75   6,414    5.00    2,672.50    131,616.25
2/1/99  95,220   16.25   128,943.75   6,414    5.00    2,672.50    131,616.25
3/1/99  95,220   16.25   128,943.75   6,414    5.00    2,672.50    131,616.25
-----------------------------------------------------------------------------
4/1/99  95,220   16.50   130,927.50   6,414    5.00    2,672.50    133,600.00
5/1/99  95,220   16.50   130,927.50   6,414    5.00    2,672.50    133,600.00
6/1/99  95,220   16.50   130,927.50   6,414    5.00    2,672.50    133,600.00
7/1/99  95,220   16.50   130,927.50   6,414    5.00    2,672.50    133,600.00
8/1/99  95,220   16.50   130,927.50   6,414    5.00    2,672.50    133,600.00
9/1/99  95,220   16.50   130,927.50   6,414    5.00    2,672.50    133,600.00
10/1/99 95,220   16.50   130,927.50   6,414    5.00    2,672.50    133,600.00
11/1/99 95,220   16.50   130,927.50   6,414    5.00    2,672.50    133,600.00
12/1/99 95,220   16.50   130,927.50   6,414    5.00    2,672.50    133,600.00
1/1/2000 95,220  16.50   130,927.50   6,414    5.00    2,672.50    133,600.00
2/1/2000 95,220  16.50   130,927.50   6,414    5.00    2,672.50    133,600.00
3/1/2000 95,220  16.50   130,927.50   6,414    5.00    2,672.50    133,600.00
4/1/2000 95,220  16.50   130,927.50   6,414    5.00    2,672.50    133,600.00
                                
                                      20
<PAGE>

5/1/2000   95,220 16.50  130,927.50   6,414    5.00    2,672.50    133,600.00
6/1/2000   95,220 16.50  130,927.50   6,414    5.00    2,672.50    133,600.00
7/1/2000   95,220 16.50  130,927.50   6,414    5.00    2,672.50    133,600.00
8/1/2000   95,220 16.50  130,927.50   6,414    5.00    2,672.50    133,600.00
9/1/2000   95,220 16.50  130,927.50   6,414    5.00    2,672.50    133,600.00
10/1/2000  95,220 16.50  130,927.50   6,414    5.00    2,672.50    133,600.00
-----------------------------------------------------------------------------
11/1/2000  95,220 17.00  134,895.00   6,414    5.00    2,672.50    137,567.50
12/1/2000  95,220 17.00  134,895.00   6,414    5.00    2,672.50    137,567.50
1/1/2001   95,220 17.00  134,895.00   6,414    5.00    2,672.50    137,567.50
2/1/2001   95,220 17.00  134,895.00   6,414    5.00    2,672.50    137,567.50
3/1/2001   95,220 17.00  134,895.00   6,414    5.00    2,672.50    137,567.50
4/1/2001   95,220 17.00  134,895.00   6,414    5.00    2,672.50    137,567.50
5/1/2001   95,220 17.00  134,895.00   6,414    5.00    2,672.50    137,567.50
6/1/2001   95,220 17.00  134,895.00   6,414    5.00    2,672.50    137,567.50
7/1/2001   95,220 17.00  134,895.00   6,414    5.00    2,672.50    137,567.50
8/1/2001   95,220 17.00  134,895.00   6,414    5.00    2,672.50    137,567.50
9/1/2001   95,220 17.00  134,895.00   6,414    5.00    2,672.50    137,567.50
10/1/2001  95,220 17.00  134,895.00   6,414    5.00    2,672.50    137,567.50
11/1/2001  95,220 17.00  134,895.00   6,414    5.00    2,672.50    137,567.50
12/1/2001  95,220 17.00  134,895.00   6,414    5.00    2,672.50    137,567.50
1/1/2002   95,220 17.00  134,895.00   6,414    5.00    2,672.50    137,567.50
2/1/2002   95,220 17.00  134,895.00   6,414    5.00    2,672.50    137,567.50
3/1/2002   95,220 17.00  134,895.00   6,414    5.00    2,672.50    137,567.50
4/1/2002   95,220 17.00  134,895.00   6,414    5.00    2,672.50    137,567.50
5/1/2002   95,220 17.00  134,895.00   6,414    5.00    2,672.50    137,567.50
6/1/2002   95,220 17.00  134,895.00   6,414    5.00    2,672.50    137,567.50
7/1/2002   95,220 17.00  134,895.00   6,414    5.00    2,672.50    137,567.50
8/1/2002   95,220 17.00  134,895.00   6,414    5.00    2,672.50    137,567.50
9/1/2002   95,220 17.00  134,895.00   6,414    5.00    2,672.50    137,567.50
10/1/202   95,220 17.00  134,895.00   6,414    5.00    2,672.50    137,567.50

</TABLE>                                                          
                                 21