Not sure what to say, I almost traded my Z due to personal reasons, I have a touring/ Sports package manual with a set of snow tires and rims that I switch each Winter/ Summer now close to 40k and the dealer wanted to give me 13K, nothing wrong with the car no carfax, only mod is the CAI and the rear fog light His reasoning wsa that in the Winter nobody wants a rear wheel drive car...so at 15K for a 3 yo older car than mine, I'd say it's better but try selling it on your own, good luck
