Oh my 9.9 isn't a Tohatsu. It's a Lehr which is basically a Yamaha save for the propane intake. Weighs 40kg, which I think is common for 4 stroke 9.9s.
Most 15 and 20s I've looked at are closer to 50kg. Tohatsu somehow has a much lighter one.
I think Tohatsu make most of the sub 30hp engines for several brands. Merc and Mariner I think. 43kg is the 20 without electric start etc but the 9.9, 15s etc are the same engine with different fuelling
So in the world of modern 4 strokes the 20s are a reasonable weight but the 10a and 15s are darn heavy.