Smoking and overheating are signs of too much prop. You probably se some black oil in your exhaist also, right? Change the prop to an 18 by 12 and you should be fine. If you prefer the performance of a three blade 15 by 10 will work and give you more tip clearance for less vibration. You will be doing your engine a a favor by doing this.
Yes, the smoke is black.
My 16x16 is a three blade prop. I like it but I do have an issue with prop walk in reverse that really makes the boat uncontrollable. Wonder if a two blade prop would help. I'll check into the 15x10.