Even with 15,000 miles, you'd like to think you could get $60-61K for the car. The trouble with a later model car is that for a few bucks more someone can buy a brand new car. I've read posts on this board about buying new Vipers for $66-68K; if that's still actually possible, then getting $60-61K for a 2001 with 15,000 miles might be a stretch.
I am still not convinced that the market for used Vipers is in the toilet. I am skeptical of sale prices I see on E-Bay, and I'm not convinced a lot of cars are actually selling for those figures. If a 96-97 GTS in good to excellent condition is selling for $50-53K, then a 99 or 00 should bring $5K more, and your 01 should be more than that. Which puts the asking price near the $60-61K we're talking about.
My take on the leftover 2002 Viper market is that there's not a lot of incentive for a dealer to give those cars away -- after all, Dodge ain't building any more of them. And a non-certificate holder is not going to be able to purchase a new 2003 SRT-10 for anything even approaching MSRP. So the $66K brand new 2002 Viper is probably a myth now.
All of what I've said above works in favor of a $60-61K asking price. On the other hand, a lot of buyers want a low mileage Viper -- 15,000 miles on a Viper is considered high mileage. There are lots of low-mileage Vipers out there for sale; someone who wants one will not have to settle for a car with more miles. Also, the number of potential buyers looking for a Viper now is low, thanks to the economy and the time of year. So while your car may be worth $60-61K, it may take some time to find a buyer at that price. If you've got to move that car soon, you probably will have to settle for less.
I've got 18,000 miles on my 2001 GTS. I'm glad I'm not trying to sell it now.