I'm with you on this one. Speculation and proof are different things, and he never showed us any proof.
Cam Prosser's 13 minutes time is based on his claim that he has lots of new tricks for most of the levels. Now maybe he does, or maybe he's being somewhat optimistic, personally I'd tend to think the latter.
That's a good estimate for a TAS run. 36 seconds can be saved on MAP07 alone, and there are a few others. [rough estimates here] MAP10: 1 sec (glide), MAP12,13: 4 secs each (keygrabs), MAP14: 10 secs (RJ), MAP31,32: 13 secs (32 can be skipped), MAP24: 6 secs (RJ). That's 74 already which makes our time 15:03.
I haven't been into speedrunning as much as I used to, but my own guess for the optimum D2 time would be about 15 minutes.
As for DOOM, here are the route improvements over Yonatan's TAS. [rough estimates here] E1M4: 1 second (jump), E2M7: 22 seconds (RJ), E2M8: 4 seconds, E3M2: 3 seconds (no plasma needed), E3M3: no change (elevator trick but BFG needed, evens out), E3M6: 1 second, E3M7: 4 seconds (exit jump), E3M8: 11 seconds (BFG), E4M3: 19 seconds (jump), E4M4: 1 second (jumps), E4M5: 2 seconds, E4M8: 4 seconds (RJ). 72 seconds, makes our time 15:00.
These are just route improvements alone. With a time of 30:03 already under 30 minutes is surely possible, mainly by shaving extra seconds off Yonatan's DOOM TAS effort.
"I can't wait to see a nightmare run through DOOM2, it's just gotta be impossible!" - John Romero