I'd guess the fastest to be approx 17 minutes and they'd be feeling sick afterwards. Depending upon the course, maybe 30 seconds faster but I couldn't see any better than a 16:30 w/o training to run a 5k and I couldn't see many of them hitting that time. My guess is the avg would be much closer to 18:00 for the top 100 ATP.
Back to using POGs. Why did I ever leave you dear friend?