Ya can't kill'em !!
I have been using the Yamaha four strokes commercially now for 3 years. I have one set of F115s on a 24' boat with 1500hrs and still running fine. All three of our boats, which we use to shuttle the fisherman to Monomoy Island in Chatham Ma, have Yamaha four strokes. All I have done to them is routine Maint. oils, plugs and filters every 100hrs. You pay a bit more for the 4 stroke, but you get much, much more in reliability and longevity in the end.
Plan on having your F150 for a long enjoyable time!
Monomoy Island Ferry