they are tyre sizes not rim widths.. but anyway like everyone else said if you must use hubcentrics not slip ons. you wont have handling differences as such but you might find the 15mm will push it out further than you want, best thing for now would be to leave them alone dont spend ANY money on these wheels be it a polish and paint or spacers save that 500 or so and put it towards the next set of wheels why fix up something u dont want anyway