I bet you could go with 6mm spacers and not hurt your bearings. That's not much difference. Now going to 15-20mm spacers is a different story.
Rubbing on the other hand is a thing of it's own. You'll have to try them to see if you have any rubbing issues. It all depends on the width and height of your tires.
I don't have experience with tires of your size on your model so I can't tell you if you're going to get rubbing or not. Can anyone else tell him if he's gonna have problems?