Sherry - you can't go by Kelly Blue Book, I don't think there are any dealers using that. That information is provided by an auction now days, wish I could remember the name of it. It has been discussed here before. A buddy of mine on this forum just bought a beautiful SRT 6 Coupe, think its an 05 and it had real low miles from a dealer in NJ for $16,000.
Like the others here have said the 15k deal gets you into your new car now otherwise you can hold out and hope you find a buyer willing to pay more.
Pat