I haven't used any external sources, just the soundpool and MIDIs. I was hoping to sell it via iTunes, but I wanted to check and make sure there aren't legal restrictions.
Probably. If you used ONLY the soundpool from MM-15, you're fine. If you used any objects from sound pool 17 or 18 (MX) (you didn't say), you may have an issue, unless you purchased the Unlimited Pro license.
Also, you are restricted from using your works in connection to any business or brand name, such as in advertising.