Neither are many of the folks here..

Anyway, have you tried pulling the specs for both the 9.9 and 15hp models? Unless the displacement & compression ratio are the same, then there’s no point in going much further. If they are, then you need to pull parts catalogs and find out just what other differences exist, in terms of valve size & timing, intake & exhaust components, ignition timing and on.

In any event, you’re asking a lot to expect a 50% increase in HP from just a carb swap.