99, 9.9 to 15

[brigeton]

I just bought a 14' aluminum boat with a 1999 9.9hp Johnson and was browsing the forums. I saw a thread about changing the carburetor and making it a 15hp.
I see the displacement is the same. Is the carburetor the only difference other than the prop?

[boats.net]

This is a controversial subject. Some say yes you can change the carburetor and get more horsepower, others say no. I have no experience with this subject.