did you try going thru the "internet sales" guy at the dealership? if not, try that edmunds.com thing of "looking for quotes" at the end of a build-your-own; the internet guys i've dealt with at several dealerships are far more aggressive with getting to a low bottom line price than regular floor sales folk.

i don't think 15% is within reach yet, but i've gotten quotes in the 8-12% off msrp range at more than one dealer in various states, and that was two months ago already.