Your phone works Great, system update, wow my phone is sluggish and yelling low memory... time for a new phone
Apple evil laughter can be heard in the background
Fixed that for you
My Note 4 phone worked better/faster after I updated it to 6.0.
Same with other family members google phones. They seemed faster after the update.
My only complaint the vendors (even Google) abandoning their older phones, and having to install non-official versions of Android if you want a newer version.
They argue that the older phones are not fast enough for the new OS, yet both the older phone and older tablet I rooted and updated ran better with the newer OS.