if you dont want the tire sticking out of the wheelwell, and for it to look clean i'd say mini tub it. i have a 275/60 mickey thompson tire mounted on an 8 inch rim with 5.5 inches of backspacing and its really pushing it.
i dunno if anyones ever fit that size tire in the stock fenderwell but i dont think it could be done, i could be wrong but thats a whole lotta tire
Theres a guy on these forums that had a blue fox stang with nitto 315 drag radials and all he did was beat in the inner fender wells, he says he didn't even roll the fenders. I dont remember his screen name here though.
that was bert306, he had nitto drag radials on his car which run kinda small anyways and im fairly sure that a 325/50/15 is gonna be way bigger cause thats basically like here is the size comparison from mickey thompson-- http://www.mickeythompsontires.com/strip_et_street_radial.html
also depends what model car you putting it on. Convertibles have the least wheelwell, followed by coupes then hatchbacks, so it might be posible with a hatch i dunno