I will share our kicker experience for the mix. We had a 9.9 on our 22. Lost the main 90 hp due to a failed thermostat housing just outside of Dodd Narrows. Managed to get through Dodd at slack to have the 90 looked at. We were on the way to Desolation Sound. Turns out the motor was not repairable as water leaking from the housing had filled the hood and gotten into the oil. It was Canada Day weekend. We talked to some shops and they smiled and asked what month we might want to come in. We went from Nanaimo to Orcas to Cornet Bay on the 9.9 over several days with careful attention and planning to tides, wind and larger ships. Worked out fine but I did feel a bit exposed on the more open sections with no back up other than a radio. Same with going through Deception Pass, although there are a lot of open fishing boats in the pass that are running 9.9 hp and they are there often!
Our 25 has a Tohatsu 20 hp Kicker. Figured we could manage the weight as the 15 and 20 were the same. The 20 was fuel injected which seemed like an advantage. I can get hull speed at about 50% throttle, so it is a lot more engine than needed. It has a "power prop". It is set up with inside controls so it is a good "get to safety" or "get to home" engine. The extra HP helps with wind or current. Having been in a bit of a spot once, I wanted a bit more safety net. Truth is I could run long distance in mild winds or currents with the 20 hp at reasonable fuel consumption, relatively low noise, good control and comfort without taxing the engine. Long as I wasn't in a hurry. So far I have not had to use it as a backup but we do run it some days when enjoying hull speed cruising, which we do quite a bit of. Doesn't qualify as a "twin" but might as a "little brother" to the 150? We are happy with it for what we do. If in areas with many other boats and one wanted a trolling motor and get to safety motor on a 25, going with the wind and the flow, I would think a high thrust 9.9 hp might work pretty well. But I wonder how much current or wind you could push. Others who have them would know better than I from their experience. 15 hp gives ample power for the 25 but if it is the same weight, a 20 hp is attractive but for the cost. The fuel injection was a bonus for me.