During the 15's do you guys perform two work sets? I have in the past.
eg. Squat 2 x 15 or 1 x 15
I don't do 15s anymore per se. If I'm doing a regular HST set up I just do clustering to 15 or 20 reps, and I usually start at a slightly heavier weight than would normally be used and only run a six week cycle. Clustering basically just means you do however many reps you can until you feel like you're coming close to failure, rest a short time and do the same thing again until you hit your target total reps, for me 15 or 20. So in the beginning with lighter weights you might go straight through to 20, as the weight increases you might go to 12, then 8, then on to 8, 7, 5, then on to 5, 5, 4, 3, 3, etc. The idea is to normalize volume fluctuations and take it out of the picture as a variable that changes. So, if you're keeping your form and not going beyond technical failure you should also be getting fairly consistent TUT.
Now, to say I've given up on HST altogether wouldn't be right be I only do the above when I need to work back into working out, like I will this weekend when I should be fully recovered from the respiratory infection. This bitch has knocked me a lot of my friends/coworkers down the last couple of weeks. Everyone sounds hoarse at the office, it was a real ass kicker of an illness that went around.
What I do now is more akin to what you see attached here in this Excel sheet. I've thrown in some numbers as examples. Basically it is an HST based routine in that it relies on progressive overload, three times a week frequency, etc. However it is strength based in the micro cycles. Basically I've found the conjugation, volume and weight manipulation in the micro cycles allows me a relatively consistent strength increase for at least the four weeks that I work in each rep range. So what I do is spend two weeks SDing, find my 12RM for each exercise, plug them in along with a reasonable strength increase to expect, say 2.5% - 5% or more depending on if I'm on anything. The just follow the plan. Once i'm done with my 12s, I'll do the same thing for the 8rep range and the 5s. The benefit here is you're always working in and around your maz weight for any given rep range while still getting a progressive overload over time as you can see in the graph. There is no need to predetermine your weights before each micro cycle, and you can extend each microcycle however ong you want in the end, so long as your strength keeps going up so it's fairly adaptable to use while 'supplementing.' Plus due to the rep ranges and how they're used volume is relatively consistent which works well for me.
Check it out if you like, it's a kick ass workout and fairly flexible. Enter weights, and exercises on this one too I believe, at the top in the greyed out area and it all populates throughout the sheet except to the graph, which might need some manual updating.