How can I downgrade from Lollipop to KitKat Not at all happy with Lollipop on my Z3 compact. My battery lasts half a day and I'm not keen on new format

How can I downgrade and get back to Kit-kat?
There is a list of ROMs available for Z3 at XDA.
Please visit the link and flash your device with an appropriate ROM and you are done. :)

Sony Xperia Z3 ROMs [XDA]