shouldnt make much noticeable difference, if they are the same price then get the 225s over the 215s. but i dont know your offsets
but depends how you drive the car. if you dont thrash it, no point staggering with only 10mm difference between the front and the rear. means you cant rotate the wheels, and 10mm each side difference isnt going to do much in any case
if you want stagger go for the 215s on the front (smaller wheel, less effort to turn) and 235 or 245 on the back to get the power down, it will fit on an E30 M3 depending on the offset of your rims.
to put in perspective, im running 235s front and 255s back on my E34 with half as much power again as your M3 and very happy with that