That is the incorrect tire size for the pony wheel on a Mustang
You should be running 225/55/16's. An alternate size that many people run are 245/50/16's.
On a 87GT at stock ride height you shouldn't get any rub with this tire size. Lowered, you may get minor rub at full lock up front. Just common with 16" or larger wheels.
The 215/60/16's are about 1/2" larger in diameter than stock...so may be more prone to rubbing at full lock
I apologize, i made a mistake with the tire size, the pony rims i want to buy are on 245/50/16. These tires should not rub correct, my 87 GT is stock height and is not lowered.
In 1991 the Mustang get the 16" 5 star pony wheels,the inner front fender opening are enlarge to clear the larger tire on full lock.
I have 245 on the 16" wheels before and they clear with years of trouble free driving,but the guy at the tire shop told me then the 16x7 wheel is a bit narrow for the tire.