I have an '07 3814 Raptor that came with the Carlisle Bias-ply grenades. After a middle tire exploded, Keystone funded the replacements. I picked Green-Ball "D" rated radials after weighing my rig and finding 12,800# on the trailer axles ("D's" were good for 15K +). A year later, at the beginning of the season, I found the tread area on 5 of the 6 tires separating, so with adjustment, I upgraded to Green-Ball "E's" and have been ok since.
I didn't go with 16's since the trailer is listed to be 13'5" tall with the 15's.