Suggest you go over to Amazon and research the products there. Bound to be some user reviews...maybe even one or two from people who actually know what they're ranting about.
That said, these two sets of cans are somewhat designed for differing missions in their lives. Once prime goal is noise-reduction, the other, while TRYING to convince people that it's a noise-canceling demon, is (to my ears) just a Type-A excuse for being bass-heavy thumper.
Since I haven't tried the QC15 yet I can't pass judgment on that design. Supposedly its SQ is significantly improved over earlier Bose N/C headset efforts (I think I read that/watched video here CNET to that effect), so maybe there's a bit of hope for Bose yet. For myself, I like my Audio-Technica ATH-ANC7 N/C headset; it's over $100 less (online) than the Bose, and for a closed-back design it sounds pretty good and does N/C fairly well. Sometimes the Apple Store B&Ms carry the A-T, so you might be able to test a floor demonstrator before whipping out the charge card if you have an Apple Store handy.
I've been looking to purchase a new pair of headphones and have basically narrowed it down to these two products. I was wondering if anyone has used both of them and could provide any insight as to which one they preferred.