Ahhh. Cog Hill #4. "The Dubsdread."
I played it about 15 years ago and thought the most difficult aspect of the course was the segmented greens. Many of those greens are clover leaf shaped, with bunkers cut up into the green surface that create the segments. As a result, greens that appeared to have a lot of square footage in reality played much smaller, as you had to be in the same segment to have much of a birdie putt.
The back nine stretch of 13-16 was indeed the heart of the course, although #15 is a pretty soft par 5. There isn't room to stretch it out so it's driver mid iron for those guys today.
#16 is a good hole indeed, particularly when you get pumped after birdying #15 and hit a hook into death off that elevated 16th tee!
#18 has got to be one of the most awkward tee shots in golf, I never did quite figure out what the right line should be. Maybe next time.