Like I said in your other thread I had the same rib with a yamaha 25hp outboard and it was a great match!
However, with just me in the rib WOT was very dodgy unless the water was very very calm! You could easily flip it!
I would go as far as to say that WOT with 30hp would simply be too dangerous with just one person in the boat! Stick with a 25hp over a 30hp outboard and your be fine!
That said I am sure a 15hp will "do the job"
IF its just 2 people in the boat. Horses for courses!