15 hp Mercury Lose of power (torque), Runs good, Good Speed poor torque when plannig

[The Miss Emilie]

I have a 15 hp. Mercury 1989 mounted on a 10 ft. inflatable. Very fast with one or two people on board, but will no longer plane with three people on board. It use to plane with four people on board. Compression is 110 in each cylinder.
Starts easy first pull, idles good, but has lost power or torque. What can I do to restore power?