The 15% off sales at GC (which are obviously great) usually occur around holidays (Memorial, 4th, Labor, etc). They usually set a minimum amount you must spend, like $299 or $399, to get the 15% off. When that sale is on, they won't bargain; that's the best they will do. Without the sale, GC will usually bargain some, again depending on how much you spend.

Like I said, I expect the next one to be around Black Friday.