No question is a silly question.
I didn't know this myself either when i was going to buy a set of winter tires. With the naked eye's estimit you can't imagine hoe 15" would fit. But it does. There's very little clearance with the front caliper (approx 3-7mm clearance) but it's ok. As long as they don't rub, you're in business.
andr3w, what size tire do you have on? and what brand tires? how are they?