http://www.tirerack.com/wheels/tech/techpage.jsp?techid=101
the guys is right you won't need any spacers because with an +15 offset your wheels will stick out like crazy, and I'm understating it.
Spacers are used when the offset is tho high for your car and there is not enough clearance. So they use spacers to push the wheel out more to clear either calipers or suspensions.
Higher the offset, deeper the wheel will be pushed inside your fenders, so the lower the offset, the wheel will stick out more.
For example, 6thgenaccord tend to need +40 to +47 offset, mostly because we generally drop our cars or just because it won't look nice if the wheel sticks out too much.
My fathers' Audi A6 2.7T would need wheels with a lower offset such as +30 to +35 so as to clear the huge calipers that comes equiped with his specific model.
So in conclusion, the guy isn't lying to you but you will look like a monter truck if you put them on.
hope this helps