Im not a tire expert at all, taking backspacing into consideration on the following---- but I think those 225's on the 15x7 will rub on the front, either d/s or p/s, probally wont rub tho if you go to a not as wide tire on that 15x7(maybe)....or a 225 on a 14" on the front. I guess thats why the nova came originally with 14". As for the backs, 15x7 can take a variety of sizes, but I think 245 is cutting it pretty close, you might have 3/8" clearance give or take from an unrolled lip area, theres a article in the nova resource pages about tire fitment.