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Think regards the shaft length the longer the shaft the deeper the V but not positive on that.
Think Mariner ,Yamaha are rated at prop ,don't know about all modern motors.
From memory the prop...

Some of the modern motors are rated at the prop ,where the older type was rated at the motor. I would think 15 horses at the prop on a 2.5m is crazy.Even if its rated at the motor its way to much....