Ok, I have read many people talk about this (not here of course as I'm new) and admit or deny it is a real problem out there.
So here is my experience.
My first Note 4 was a unlocked TM Version. It lagged so bad I had to take a valium to use it.
I could literally type and finish typing two words, and then the keys would pop up and the letters appear.
Same with th. S pen.
There was a serious lag between a touch and response. It Was infuriating.
I am not clueless about phones so I did everything I knew. Even rooted it and tinkered. Had actual developers help.
Nothing.
So, knowing it would probably be a waste, I turned to Samsung and did everything they asked, and even in Safe Mode lagged.
As a last resort I took it to a Samsung store and the rep even got frustrated with it.
The rep said it was a "lemon" and definitely a defect.
Now with my 2nd there is no problem.
If this is an issue then definitely swap it out. If you are gonna spend this kind of $ get a phone that is right.
To be clear I am talking about true lagging issues not the normal here and there hiccups that all have ( FU Touchwiz) now and again.
John 3:16