Don't do it!!!! I did and regretted it big time. Not only will it not get the boat up with any kind of load but if you come from a place with ethanol fuel
you will have nothing but problems with the low speed jet varnishing up even if you do run it dry every time you use it. It was one of the worst purchases I ever made.
A good option might be the Honda
20hp which is the same as the 15 except for carburation which gives it the extra umph. Both of these are very light motors which are easier to handle.
Personally, I went back to the Yamaha 20hp 4 stroke
but we have electric
winches so pulling the boat up onto the davits
is easy for the wife and I. Once you can put 4 in the boat with a load of groceries, fuel, etc and still plane you will never be happy with less.
Just my opinion.