Wife asked an interesting question...

I don't understand the 90 minute breaks.

my longest day was a simulated a little more than 70.3. and i raced IMAZ, goal was 11 but got sick the week of and finished in 12 and change.

2km swim - 32ish
60mi bike - 3:05ish
13.1mi run - 1:52ish

Interesting concept. That would be a 12-13 hour day, I personally wouldn't want to do that but if it works for you then that's all that matters. If I "rested" for 90 minutes after a 6 hr bike ride there is no way I'm getting back up for a 2 1/2 hour run.

To the OP my longest training day will be a 6 hour bike (Fitzgerald Level 6 plan).

I don't understand the 1.5-2 hour swim?  for me, that would be something like 7000 m?

Hah!

Yep, I did something like this two month out and then a month out from IMLP. Not sure it would have much use for someone looking to PR, but as a first-time Ironman, it REALLY helped my confidence on race day, especially since I did it all on the race courses. I considered it my "secret weapon" for getting to the finish line.

As others have said, that is a very very BAD idea!  The recovery alone from this is going to be equivalent to your IM race day (read: 3-4 weeks).  There is absolutely no reason to do this workout above, especially if you are looking at a 15+ IM day.

In my 5+ years of coaching I have never come across an athlete I have trained, consulted or spoken to that this workout would benefit.  Not one.  I believe you may want to review what that workouts really calls for.

If you're going to do a race simulation, I would recommend a Saturday with a 4500m swim, then an 80 miler at IM effort.  Follow that up with a Sunday workout of 50 miles at IM effort and then a 10-12 mile run. 

The above, IMHO, gives you the necessary confidence (fatigue-wise) and also forces you to address nutrition and the mental aspects of an IM race day while not causing you to have to recover for more than a couple of days.

But as others have also said, YMMV.

My plan was the same thing as the above.

I tend to do race simulations for sprints and olympics.  I imagine your advice might be different for those (even if you disagreed with doing race simulations).  What would you recommend for the HIM distance?  Currently my race simulation is every Sunday, with a 2000 meter swim, about 40 mile bike, and 7 mile run.  It seems to not wear on me - but I am interested in the wisdom of doing this.  For my Sprint/Olympic distances, it was no drain at all and seemed to be the reason I propelled from zero to age group podium last summer.

Agreed, sounds like doing nearly an ironman in order to train for an ironman.

A HIM is a great indicator of your fitness for IM if done 6-7 weeks out, but not a great race simulation.  I like this window because it allows for you to still fix things if needed right before your ramp up.  If you are not doing any race simulations in your training, then I suggest you review that.

The weekend given is a great gauge of where you are for IM day (if done properly) and I would do this about a month out from the race. This gives you time to make any adjustments (mostly nutrition-wise) in the next two weeks of your peak/race specific build before you hit a 2 week taper.

The biggest mistake, IMHO, that most IM athletes (novice and experienced) make is not practicing EXACTLY what they will do on race day nutrition-wise, pacing-wise and even clothing-wise.  This should all be nailed down more than a month before the race and practiced practiced practiced.