It's most likely a full carb swap, but it could be just the jets, if so you will need to adjust the new idle mixture after fitting the new jets (YouTube carburettor mixture) I'm not sure on your model if It can be derestricted, I think it can, but I can't remember for sure I've derestricted many many outboards in the past, the last suzi I done was a 4-6hp I think, and that was jets if I recall rightly, before you start make sure both models in question have the same bore/cc then check part numbers for the jets and carbs, if the carbs have the same part number then you will find the jets are different sizes, if not it's a 15 carb you need it could even just be a restrictor plate between the carb and block if your lucky check that first!, it could be a simple stopper on the carb full open position to stop it opening fully. Also check that the reed valves, exhaust tube and or restrictor (if it has one) are the same part numbers if not they will need changing as well to get the full 15 back.
But this all cost money and on these old motors, you will break parts, thread and snap bolts and will need new gaskets, my advise is if you think you need a 10hp just buy a 20hp anyway! Very little in weigh if 2 stroke and you don't have to use the whole 20hp power! Better to run a 20hp half power that a 10hp full all day! Derestricting engines is often not worth it unless it's a real minter, but such activity will gain you valuable outboard engineering knowledge that's handy in the future
