My thoughts...and I've got a 3.8 Quicksilver with a Yamaha 20hp, my boat has the Ali floor. The boat weighs 100 kg and the engine 50 kg
Its certainly more than fast enough with this engine, and I'm sure it would tow a ringo fine.
I'll agree with what Matt said about the weight, we now have our set up on a trailer, as the engine is too heavy to carry more than a 10-20 feet on your own. It isn't the dead-weight of the engine, I'm sure we could all have a go lifting 50kgs at the gym, it is the size of the thing you are trying to pick up!
The boat is great for what we use it for, as we can have it on the trailer, the putting together, inflating, deflating and getting in the car shouldn't be under estimated with a SIB of 3.6 metres and above.
If I didn't have this option, I would be seeking out a used Bombard Aerotec 380.
In hindsight, I would have preferred the 15hp for the weight power trade off.