Depends what you want to get out of the session. Either way, you're doing 1 or 2 miles warmup, then session (which is 15 miles with maybe another two miles of floating), then two miles warm down. So that's 21 or 22 miles, a massive workout.On that note, Terrier, I was half thinking of turning the Daddy of them all around.... And making it 1,2,3,4,5. I'm wondering would that be too much though. I also think the 3x8k with 800mts steady - not easy - between is tougher than the aforementioned Daddy.
The way I always looked at it, the session is all about form and quality - technique and fitness combining to give you the prefect marathon test about 1 month out from the race. The feeling of excitement also builds through the descending numbers - by the time you get to 3,2,1, you're flying, and the pieces come super-easy. You're almost laughing by the time the 1 comes around. Pass the test, and you have super confidence coming through the last 4 weeks.
The 1,2,3,4,5 might be a session you'd run earlier in the program - maybe 8 weeks out. It would be a slog, but great training if you can handle the MP OK.