An FDR is a Factory Data Reset. It will not return your phone to the previous Operating System, but it cleans out any leftover code from the OS upgrade. An FDR can sometimes help with various issues after an OS upgrade. The downside is that it erases all your data, so you have to back everything up ahead of time and then set your phone back up after.
Yes, there were several changes to how things work with the update to Lollipop. Some of the things that may be making the battery drain are the Facebook and Facebook messenger apps; if you aren't using them, uninstall them.
As for the preloaded apps that you aren't using ... unfortunately, you can't uninstall them, but you can disable them and then they won't appear in your app drawer, i.e., settings > applications > application manager > scroll over to the All tab at the top of the screen > scroll down to the app that you want to disable > tap it > uncheck Show Notifications (so that you won't get bugged by the Play Store to update it) > tap Force Stop > tap Disable.
One thing you may want to try is a System Cache Clear; it may help some of the issues you're having, doesn't hurt to try, and it shouldn't erase any of your data, i.e.,
Power down phone
Press/hold volume up and home keys, then press/hold power key
When phone vibrates, release power key
When system recovery menu displays, release volume up/home keys
Use volume keys to navigate to wipe cache partition and press power key to select
Once finished, press power key to reboot system
