As Tomek said, 8" of wheel with a proper sized tire is about the limit as to what will fit without a lot of work. In fact 15x8" ET22 with 225/50/15 tires will likely only rub slightly in the rear (semi-rolled lips from the factory back there), so there is little work involved.
If you really want to jam as much tire as possible into the fenders, 17's are the way to go. There is more strut clearance as you go upwards, and the tire choices are much better. Shoving 245's all around with 17's isn't very difficult.
Also, keep in mind a stiffer suspension means more rubber. I'm running 225's on an ET25 wheel, and I have never rubbed a thing.