I quite like my 6S Plus.
My last phone was an iPhone 5 so I was a little worried about "pocketability".
I'm a man so I generally have large pockets in my trousers. I don't wear baggy jeans, not skinny jeans either, just regular straight Levi jeans (tight around the ass/thighs and loose around the ancles) and I find I can easily fit the Plus in my pocket.
As long as it's positioned at the side of my thigh I can keep it in my pocket while sitting without discomfort.
But it is a royal pain in the ass to get the phone out of my pockets while seated.
I really like the added screen real estate. Web browsing, looking at photos, playing games and reading e-mails really is a joy.
As for one-handed use, I can easily use the phone one handed while standing still or sitting. I find Reachability helps me a lot. But I don't feel safe using it one handed while walking, it constantly feels like I'm about to drop it.
The optical stabilization in the camera gives it a subtle edge over the normal 6S.
I've tried filming while riding along in the car and the stabilization can really make a huge difference.
I love that I can use it pretty much uninterrupted in landscape/horizontal mode.
I can't comment on how the battery life compares to the regular 6S, but I can say that it blows my old 5 out of the water. I can easily use it quite heavily all day and still have a good 30% left when I go to bed.
With normal, non-intensive use I can actually go two days before needing to charge.
-but, I don't really do "non-intensive", I find it very hard to not fiddle with it all day
One thing I hate though, is the keyboard in landscape mode.
GOD HOW I HATE IT!
Instead of giving you larger keys, it stuffs "handy shortcuts" around the sides and leaves the tiny-buttoned keyboard in the center.
I have large hands and I can just reach the center keys with my thumbs but I can't write a sentence on it without hitting those damned useless shortcuts.
Shortcuts like "undo" that is positioned one key away from "shift".
Guess what happens when I want to type a capital letter?
I undo EVERYTHING I just wrote

Really hope Apple adds an option to just use a regular enlarged horizontal keyboard without using "zoomed" mode.
So as a guy with large hands and big pockets I can recommend the Plus
As for lag, I have experienced none.
I set up my 6S Plus from my backup of my old 5.
Read if you are worried:
https://forums.macrumors.com/threads/6s-plus-pauses-freezes-lag-serious-issue.1921141/
People on that thread are having issues with lag but I haven't taken the time to read through it.