Go on there type in old sizes type in new sizes go outside and see how much room you have and here this will help…s13 has MAX backspace Front~ 150-159mm MAX backspace Rear~ 172-179mm
my advans are 17 x 9.5 +19, and i run zero camber in the rear with a fender roll and slight pull. so i would see you have no issues running 17 x 9 +15 in the rear. the rim edge will probably sit flush with the fender.
Its all about what you consider flush… this was flush to me this spring… now I wish I woulda got Battles instead of the weapons at 17x9.5 +15 all around or staggered 17/18
LOL I tried the backspace is how much room there is between the hub and suspension… and on that site it will give you info on how much of an increase the wheels are going to be from stock to whatever you go with so you can go outside see how much room there is left. For example say you got 16x7 +40 and you have like 2" left of room and you type in your new rims lets say 17x9.5+15 it will tell you how much the increase will be in both directions…