For what it's worth, after having 4 iPhone 6s Plus units doing the homescreen freeze, I just got a 6s the other day, and I'm also getting lockscreen freezes on it, though not nearly as often. In fact, I got one or two the first day, then NONE the second day. And today, the third day, I had a bunch of freezes this the morning.
I set this up without much thought though. Got it new out of the box, updated to 9.2, reset and restored from the iCloud backup from my 6s Plus. The 6s Plus that created the backup was completely free of lockscreen freezes.
I just did a DFU restore on the 6s and I'm setting it back up now as New. Which is a pain, but that's what I had to do on my 6s Plus, and it fixed all the freezing.
So, not sure if it makes anyone feel better, but it's not only the Plus, and it's not directly tied to 9.1, because this 6s on 9.2 is doing it too.