He must mean 15mm rear as the M3 has a lower rear offset. The 40mm offset wheels should work with no problem. I would be a bit concerned with rubbing on the 15mm offset version, but if you're able to keep those in the rear there is a chance it would fit without rubbing with 225/45R17. Spacers would push them out further and make rubbing worse.
Refer to 'Rudy/E46Fanatics' as your previous contact when you order online. Credit E46Fanatics.com by clicking here.