The golden rule here is Displacement = Torque= Prop diameter X pitch. or as is often said, there is no replacement for displacement, or no substitute for cubes. 

Be wary of HP figures, remember HP is a product of Torque and revs, some engines get their HP just from revving harder and subsequently have less mid range Torque. Others do it with cams and engine control, such as Yamaha, be aware these engines are working harder to give the Hp you think you are getting. The Merc 135 is a 3litre V6 as others have said, while the Honda is 2.3 litre straight four, and the Suzuki is a 2 litre straight four, that performs very similarly to the 115, but has about 300-400 top end revs, maybe a little more mid range torque. Note that only he Yamaha, Suzuki and Merc fall inside your stern weight limit.

Have a look at Spence's thread here where he compares modern 150hp engines. He uses this (https://www.arb.ca.gov/msprog/offroad/cert/cert.php?) website to get all his numbers and mid range torque numbers. 

Incorrect the Mercury 135 is an inline 4 cylinder not a V6, the Honda is a 2.4litre not 2.3. Honda 150 and the Yamaha are the same weight 220kgs.