Gents,
5, 6 and 15 greens, all Fazio greens, were altered two years ago. 5 was completely re-contoured, and a chipping area was added short-right of the green. A large "wrinkle" in the left side of the 6th green was flattened. 15 was completely rebuilt, with a new green, new bunkers to the left of the green, and a new stone wall holding up the green from the pond. Other changes were proposed, such as softening the 2nd and 13th greens, but these were nixed by the membership. There is mixed speculation about whether these changes were for the PGA Championship or for everyday membership play.
Overall, though the course has not changed much over the past few years, and 5, 6 and 15 are still very much the same holes. In my (unsolicited) opinion, these holes need to be rebuilt by another architect. 15's green gradually sinks into the pond and has to be rebuilt once every ten years or so. Moreover, 15 is all but unplayable for anyone worse than scratch. 5 and 6 are not much better. And, of course, Oak Hill needs to take out more trees. I think Philly Cricket would serve as a great model for that project.
That being said, expect the course to be phenomenal condition for the PGA. Jeff Corcoran does a great job with the turf maintenance, especially when it comes to the greens.
Matthew:
Yes, what you call "the original 5th hole" is still maintained as a practice hole. It's a great place to spend a few hours working on your short game shots. However, this par three is actually not original at all. The original configuration had 5 playing in the current corridor for the 5th hole, run north to south. The original 6th was a short, bunker-ringed par three, playing southeast to northwest to a green located near the current 9th tee. They abandoned this hole (although left the green for awhile) before the 1968 U.S. Open, replacing it with the new par three that currently serves as a practice hole. The original 5th then became the 6th for that tournament. All of these holes were abandoned and/or destroyed when the Fazios re-did the course in the 1970s. That practice hole (nicknamed "The Short Stop," which I always liked) is occasionally used as a sub when another hole is closed for maintenance.