To clarify:
going on the Disney site will only get you the Disney discount. In order to get the additional 15% on top of that you need to book through Orbitz. The 'base' prices there already include the Disney discount, and then the discount code gets you the additional discount on top of that.
For example, I've been pricing my trip, and 7 nights at All Star Music on the Disney site with their discount is $618 for my dates, and on Orbitz with the additional discount it would cost me $529
If you specifically want the meal plan I don't think that would work, but you would also have to assess if the meal plan is a financially-beneficial idea.