I've heard of some older 20 footers with a 140 on them. With the exception of the Yamaha 150 four stroke, (4 cylinder) anything less than 150 was a 4 cylinder and 150 and higher is a 6 cylinder. Imo, the 6 makes all the difference. It's not just a matter of 10 or 20 hp, but a big difference in cubic inch's, (torque and power).
With a light load, 2 people, half fuel, etc, it might be ok, but when you've got 4 people, more gear, fuel, etc, I think you'll be putting a heck of a load on that motor. Not to mention, when it gets rough and the extra power you need won't be there. If it were me, I'd want nothing less than 150 on there.