I am running 15fr 18r on my e90 328i with sports, and with my staggered 17's, they will rub on the back if REALLY run hard through some whoops. Same with the 19's. Both oem rims and tires.
I am considering going 12fr 15r, but there are some hubs that won't allow 12mm spacers, I think. Or maybe it is 10mm. Need to figure that out.
15's on front work well enough, but I think it might look a little better if they were to be tucked in just a hair.
Also, you got a coupe or sedan? As I understand it, coupes have slightly less room out back.