The good thing about portable 2 strokes Tohatsu is that all (3) 9.9-15-18 HP weight same 40 Kg, if in need to reduce power you could detune it to any of the 3 mentioned models outputs. It's as simple as adjusting an internal throttle limiter screw to achieve controlled throttle if needed in small sib uses up to 9.9 engines.
Besides this, you could grow into a larger sib/rib and maintain same engine. Started using a 18 HP 4 years ago and that nice punchy engine has moved nicely 320 to 420 mt. sibs and know moving a 430 rib. Ain't that super cool, one for all, all for one...