With a 15" tire/ wheel combo you can look to weld wheel web page to find the specs, with a quick google search I found a half dozen resources for fitting wheel/tire combos on a fox stang, been done a bagzillion times. I understand you are looking for a specific 'this is what fits' answer but most cars here have not used a 15 wheel tire combo in years, with the possible exception of a couple drag cars.
go to the fox picture thread and look for the combo you like and see if they have specs in a thread here.
pics of how your foxbody currently sits
www.stangnet.com