I use a 15 and would like more power but the simple fact is the 25 is much too much of a (man)handle to cope with over beaches, out of the back of a Land Rover etc. Consider the fuel consumption too.
The 15 is a great compromise, cheap to run, easy to handle, will cruise at 16 kts + and will even pull a young skier.
Someone mentioned a 20 4 stroke - I would definitely look at the latest Suzuki 4 stroke model as an option now, superb reviews out there - very lightweight (for it's hp), quick on pick up and very economical.
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