From the margin I have with the 215/60R15 tires, I think 6.5" rims should fit 225/60R15s without too much problems, just the speedometer will be a little bit off (2.6% slower than actual), 225/55R15 could be better.
The tolerance that I heard was +/-3%, I think even new and worn out tires may bring 2% difference.
99 BMW 540i 6-speed 110K Km
03 SAAB 9-5 wagon 80K Km
92 400E (Sold) 245K km
Still missing the days with the Benz, it kept me busy.