I have a 2012 and it is one heck of a truck. I pull 14K+ 5th wheel and there are times that I have to look to make sure it is still there. So far with 18K miles pulling the trailer, I am averaging 14mpg. Without the trailer I am looking at between 19 and 22 mpg. I also think that one can not upgrade the 2012 to the 2015 version as they have changed a lot on the top of the engine and also the turbo. At least that is what I have been told and read on other forums. I would get the 2012 if I were you and save the depreciation of the 2015.