I switched mine last week.
Took about an hour to optimise all the apps.
Phone seemed very laggy to use so something wasn't right so I switched it back. Strangely it didn't optimise the apps again and took a matter of minutes to reboot.
May give it another go at another date, but I've not had any complaints with the Note 4's battery life so far and I'm a pretty heavy user as its my work phone. Without charging during the day I'm probably at about 40% left after 14-16 hours, with mixture of exchange email, SMS, spotify, twitter etc.
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