I just factory reset my Nexus 6 and it is much improved.
It took a long time to erase data. I believe it is because it's encrypted.
What was interesting is that there were no operating system updates required (that I could see or had to ok). The reinstall of a hundred plus apps seemed to not slow anything down as I took the opportunity to configure some settings.
I did have to add my credit cards back to Android Pay.
And I took the opportunity to enable face recognition to unlock the screen. I hadn't seen that option there before. It's working very well.