size of motor for smokercraft bigfish

[just4phun]

So I finally got a boat (woohoo) a 14ft Smokercraft BigFish but it did not come with a motor. I have an old Merc 7.5hp on it right now, it does not plane and is very slow but it does get me out fishing. I am currently looking for a new motor but not sure about the size (hp?) I should get or 2 stroke vs 4 stroke.

Any suggestions? Is a 4 stoke the way to go these days? Is a 15hp 2-stoke similar to a 20hp 4-stroke?

Thanks,
Just4phun