2016 Cadillac CTS is the newer version with some differences, such as the horsepower and fuel economy.. And finally, a bigger engine usually means less mpg. But the 2016 Cadillac CTS has a more powerful engine and it gets 1.3 more mpg than the 2015 Cadillac CTS. Among similarities are the body structure, market segment, starting price, ground shadow size, height, and maximum occupancy.