2 week vs. 3 week IM taper

I've done both.  

Although, I can't really argue for one or the other.  There were/are SO many other variables in choosing your taper.  I did a 2 week taper for IMFL and a 3 week taper for IMLOU & IMLP.  It MAY of had to do with the time of the year.  FL is a fall race, cooler weather toward the end of training and I felt like a 2 week taper was enough.  For both LOU & LP, heat of the summer training, and I was exhausted and felt like I really needed a longer taper.

My FL time was the best of the three, but definitely an "easier" course (and cooler weather) than the other two.

There's nothing wrong with following the plan. You have, mostly, -ish Stock plans are just that: stock. They'll do the job but if you're looking for an ideal taper, it really is dependent on so many factors, including you as an individual. The number of days or weeks is just one. I can see from your logs what you've been doing, but not how well you feel you've responded to it, and how you feel now. (And those are only three more factors among many).

Also, ideally, you'd have somewhat different tapers, consisting of different workouts with respect to both volume and intensity for run, bike, and swim.

Training adaptations (let's say the beneficial ones of the kind you're looking for) can occur anywhere between a few days to a few weeks after X.

Here are my vague thoughts (definitely worth what you paid) with regards to you: if at this point you're asking about a two or three week taper, you're probably not so blown out from accumulated training that you'd be asking (you'd just be thanking God and the BT plan for a three-week taper).

If anything, you've gone slightly under what your plan calls for (I'm hoping you didn't all out race-race that little race you did today, congrats btw). That would incline me to a somewhat shorter taper, since you don't need all that recovery time. Looks like you've (recently) done nearly equal amounts of cycling and running; that would incline me towards continuing to peak out cycling until about 10-12 days out from the IM (meaning you haven't done a lot of cycling--relatively speaking--and you still can). You're a strong swimmer; do whatever you want there. You don't need any kind of a swim taper. You really haven't done enough swimming to warrant it (whether you're a strong swimmer or not). Running I might do whatever's on the plan, or if you're feeling just awesome, you could do another long run (15-16mi, figure pulled from thin air) next weekend (two weeks out).

Remember that during taper you're (generally--there are all kinds of tapers) reducing volume, but intensity should be around race pace. Which, for a first IM, is still not particularly fast, so possibly closer to your LT paces if you know what those are.

Again, most of this is a shot in the dark ... it's just random thoughts about taper and you.

In a nutshell, if you are doing tons of volume, go with a 3 week taper.  If you're doing what 85% of those out there are (and they think it's high volume), go with a 2 week taper. 

The 3 week taper was brought from marathoners that went into taper over-trained so they needed the 3 weeks.  Unless you are doing basically 20+ hr weeks, then you're 'probably' good with a 2 week taper. 

And for the record, if you're doing 20+ hr weeks and not a pro, then you're doing it wrong.  (MY Personal Opinion).

The biggest mistake I've seen with people tapering is that they reduce the volume AND intensity.  Reduce the volume but maintain the intensity.  That's how you stay sharp and reduce your fatigue levels.

Good luck!