You do realize that you just said that Carnoustie's 18th averaged 4.6 and ANGC's 15th averaged 4.8. Given the extra 31 yards, that means the scoring on them is pretty much the same.
Par is irrelevant, if it weren't for the tradition at the Masters with eagles on the back nine thanks to Sarazen in '35 and Nicklaus in '86, ANGC would have had the option of making 15 a 500 yard par 4 instead of lengthening it to 530 and keeping it a par 5.
I should have said "in some ways" ANGC's 15th is more penal. At Carnoustie if you choose to play for a 5 it is a straightforward hole and the 5 is easy to get. At ANGC there is no safe 5, and it breaks the risk/reward equation by making the "risky" option of going for the green in two perhaps a more conservative play than laying up!
Doug, once again I haven't played either of these holes, so take my comments for whatever they are worth. I thought you could get a relatively flat lie if you lay up on the right side at ANGC 15. The green complex at ANGC also looks a lot more receptive to me. There is less penalty around it, no OB, and more options to recover if you miss long, left or right.
Pretty sure I've read the R&A put the tees up at 18, so it didn't play to 499. Those 31 yards may have been more like 50 or 60 yards.
And par and the shorter distance are not trivial, IMO. Virtually no pro's go to the 18th at Carnie thinking "I want to make a 5." They don't willingly make it a 3 shot hole. Even when they hit iron off the tee they expect to go for the green, probably with another iron, as Sergio did on Sunday. Not so at ANGC 15, which plays as a 3-shot hole for plenty of players. If they hit iron off the tee, no one would get home in two.
Pro's play ANGC every year. I don't recall 15 destroying the chances of anyone near the top. Seve, e.g., was still tied for the lead in 1986 after he holed out there. Yet in just two Open Championships, the 18th at Carnoustie has been a train wreck for one top competitor after another. Six players came there with a chance to win. Only one managed par or better. They played it in a collective 31 strokes. An average of 5.166. That would be pathetic on a par 5. On a par 4 closing hole, I bet that is unprecedented in the majors. I also bet it's a helluva lot higher than the guys challenging at ANGC average the last day.