Phil Robertson -- Marry 15-Year-Olds -- They Clean Ducks Good

Reinstated "Duck Dynasty" star Phil Robertson thinks guys should marry 15 or 16-year-old girls because when they get any older they become gold diggers.

Another video of Phil's preachin' has surfaced ... and in this one he implores his followers to marry young girls because "They'll pick [clean] your ducks." He goes on with a cautionary message: "You wait till they get to be 20 years old ... the only pickin' that's gonna take place is your pocket."

So we gotta ask ...