Thanks Alex!
The smallest size rs's come in is 6 x 15.... but you might have trouble finding them as they where originally sold for this.
Your best bet is to find a set of 15 x 7's with appropriate offsets for your car. You can easily stuff them under your fenders but you might run into turning radius issues with a 15" as it will probably come into contact with your front swaybar/control arms.
Go through this list and try and find some that will work for you, and then begin the hunt for a good used set. I searched for a good 4-6 months before I found the ones that I wanted.
Mine
RS157 7 x 16 49.0 130.00 5 71.6 Porsche 924 S,964 VA
RS158 8 x 16 49.0 130.00 5 71.6 Porsche 924 S,964 VA