We have a 2015, same model. Your trailer is at least 13' 2", pretty much guaranty that's the minimum. We had 2" risers put on two years after getting our trailer due to the difference in bed height of our new (than) truck. Our trailer sits closer to 13" 4" now. DON'T guess, like others have said take a straight edge and level and measure to be sure, you don't want to find out the hard way! :S
This is how it should be done. BTW this is NOT our trailer!
Dan