15 is ideal for a 1436. They often don't like too much extra motor weight, and especially in the case of Johnnyrudes, the weight difference of 9.9s and 15s is usually less than 5 pounds. What is the matter with the motor on it?
I am not crazy about the B&S motors. Yes, they are simple, but they are noisy, and are basically a lawnmower engine mounted on a lower unit. For small outboards, I see no reason in the world to stray from 2 stroke motors, unless you are really into real slow trolling, and don't want to use electric for that purpose.