How the heck does it cost $800/month for the SVT? I had a 3 year loan with little down, and my payments were only $450/month. I got in at 0.9% financing, which helped, but it shouldn't make a world of difference. I'm assuming you're including insurance, but how much could that be?
No offense, but you're not going to get $15,500 for your car. The SVT market just sucks. A mint 2000 SVT with 18K miles and a 100K mile warranty just sold for $15K even, and that was a bit higher than the norm. Your best bet would probably be to sell off your mods seperately, and then sell the car.
Good luck, whatever you decide to do.