Sorry folks! I don't know much about the sales arrangement, but as some of you mentioned, it would seem that it takes 3 sets to get all 15 cards. It would also make sense that a checklist appears in each set, but I'd need to touch base with Topps to confirm that. There is no wrapper for the set.
By the way, there's a few items that I don't see shown in the promotion, so maybe they're saving these as a surprise? Don't know yet, but I'll try to find out soon...