I myself prefer to run an APC 14x6 on my Hog Bipe using the O.S 91 Surpass, but a 15X6 will work also if thats what you have on hand. Probably tach in the low 9's with the 15x6 instead of the high 9's with a 14x6. Either prop would be fine for maiden flight, and you can always try the other later to see which one you prefer and which makes your engine happier.