In my informed opinion I would guess that perhaps a couple of ATP players could run a sub 16:30, despite their training and musculature. I say despite because I bet none do comprehensive lactate threshold work as part of their training.
Out of the top 100 many would run in the 18's, most in 19's.
The truth is that high level sports is about specialism. I was a little surprised that Murray said he ran close to a 57 second 400m all out (which is pretty poor) - meaning his capabilities at 400m have probably already dropped significantly from his likely capabilities at 100m. The 5k might be even more surprising.
I'm probably a good example - being more of a 'sprint-type' my 5k time is far worse relatively to my short distance times, even if I train for it.