You may want to look into a wheel wax if you haven't already. It should cut down wheel cleaning time substantially.
My favorite wheel cleaners are Auto Finesse Imperial and Sonax Wheel Cleaner.
Regardless, I find myself scrubbing a little every time I wash.
2002 E46 M3 6MT | Jet Black . Black Nappa | My Build Thread
2009 E90 M3 DCT | Melbourne Red . Speed Cloth