The problem is in your loan-to-value. With $2500 underwater on a car worth $12000, that's 121% loan-to-value, and out of the range for almost any lender on a used vehicle.
15% is a staggering rate, definitely see why you want to refi that one - but you'll need a lower LTV... is it possible to make a principal payment in the range of $1000? That would lower your LTV to about 112%, much more feasible with lenders. And are you dealing with the actual payoff amount, rather than the remaining balance? With a high interest rate, early payoff may actually cause a fairly large reduction in amount due by causing elimination of interest, especially while the loan is relatively new (you primarily pay off interest in the first couple of years, and principal later in the loan life).
