the guy was only about 6'9" or 6'10". so the JR was more doable probably. I don't see why you couldn't hit 15 JS & 10 JR. As the JS should be a lot easier/quicker to train. i once had a 6'2" center that put up to a 11-12.5 ratings & he had a couple 10s in center skills.
I think 6'10 is the perfect height for this type of thing. According to the training calculators, 6'10 is the cutoff for decent pops in big man skills. 6'9 supposedly has a noticeable drop off. I've trained a 6'7 guy in big man skills, and it's definitely slow. 6'2 must have taken ages to get those 10's.
But I imagine 15 JS and 10 JR would make him an utter beast at PF or C for 3's.