2016 Lexus RX 350 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 Lexus RX 350 has a more powerful engine and it gets 2 more mpg than the 2015 Lexus RX 350. Among similarities are the body structure, market segment, starting price, ground shadow size, height, and maximum occupancy.