Pete, Thanks for clarifying! I just assumed it to be a typo because of how nicely the 15 miles fit with his previous editions cap of 15 miles at marathon pace. I do realise that doing 15 miles at tempo pace (hour race pace) is doable because it's broken up. Sort of like people doing 10 x 800 meters at 5k pace. More volume is done because it's broken up. I agree it must be done with a lot of rest around it as it is quite stressful.
Another thing I notced was that these workouts also placed time limits of sorts on them. It assumes the runner's T pace is 4:45 to 5 minutes and said to adjust accordingly for slower paces. So the 5 miles at T followed by 5 minutes for someone such as myself with a T pace of 6 minutes would be more like 4 miles (24 to 25 minutes) followed by 5 minutes easy. Then maybe 3 to 3.25,(18 to 20 minutes) and so on.....
So this workout for a slower runner would not be 15 miles at T pace, but would still be 70 to 80 minutes at T pace. That would be about 12 to 13 miles for me at 6 minute pace.
Thanks again for the clarification!