Thanks to the helpful replies & the, OP your a bell-end replies.
I've spoken to a few people at the weekend, mainly marine engineers & the like from various shops.
The overall opinion was that a 15hp would'nt be the best way to go, but i should be fine with a 9.8 or such as long as i'm careful & keep an eye on things!
For the record the boat is a SIB & apparently the power rating is a for a 4 stroke motor, whethe that is true or not i don't know.
For the ones portraying i'm some sort of fool, it might be bread & butter knowledge to you but to someone who's a beginner it isn't so obvious!
Anyway, the search continues for an OB!