Re: force propeller question
No, you should not need to put the ring back--I don't know why it was put inside the prop in the first place.
Depending upon the size of your boat, the 13 1/2 X 15 may or may not keep the engine in the correct RPM range. HOWEVER it is almost a certainty the the 13 1/2 X 23 will be too big for your engine unless your boat is a very small racer type.