Share your experience!
moved your posts together to better addressed your issues/concerns
1. memory, there's nothing you can do about it as Lollipop it's heavier because it uses ART.
As I've posted and Rickard has confirmed
19 hours ago
Lollipop takes up more space so it's normal that you have less available storage after the update. As s4alon says, one of the reasons is that Lollipop uses ART instead of Dalvik.
2. as going back to KitKat, you have 2 options
a. contact your local Xperia Care
http://support.sonymobile.com/global-en/contactUs/
or
b. use flashtool
3. Battery
4. Lag
both issues could be tackled if you reinstall lollipop with PCC, make sure it's a clean install, which means delete all the apps and data, keep in mind that Lollipop it's a major update and it's wise to reinstall it, it will smooth things out.
Bridge (for Mac)
Alternatives on How to backup Xperias
http://talk.sonymobile.com/thread/36355
Also,you could have posted in the original thread with problems as these things have been discussed already. Topic locked.