4" backspace would make it worse. What kind of calipers does the kits have? I find it odd that the 6 lug Rallye does not clear, considering that they were used with disk brakes on the oem application that used larger calipers than most of what is offered in the aftermarket. Perhaps you need to bump up to 16" wheel fi they're using later style dual piston calipers, which the 15s will not clear.
