I have a set of 265/55/15 cheater slicks left over from my 5.0 days.
Does anybody know if there is a 15 inch wheel I can use to put these
on a 95 Z?

 

You can get 15" wheels from Weld (Pro-Star and Drag lites) that require some grinding of the rear brake calipers. Then there are wheels from Centerline (AutoDrag and Telstar), and from Bogart (high $$$$$) that fit with no modifications.

With the 265, you would probably want a 15x8" wheel with a 5.5" backspace.

There are writeups in the FAQ covering the Welds and the Bogarts.