Several monthes ago Sony started to push Android Lollipop 5.0.2 to their Xperia Z line phones. After upgrade some customers started to complain about battery and system performance in their phones.
For example if Xperia Z2 or Z1 compact could work up to 2 days with single charge, after lollipop they hardly can work 1 days.
Or in kitkat versions Xperia Z line phones work too fast and smooth, but with Lollipop versions they work slow as low-end smartphones.
So for both cases i tried 2 experiments(i am using z1 compact) and both gave great effect.
1. For battery. Go to settings-power management-stamina mode, and use exactly this configuration:
You can add IM messengers, email apps to App active in standby section.
2. For system performance: Just clear cache partition data. It will not remove any personal data, it is just cache data which you don’t need. And for this operation you don’t need to open boot menu. Just press and hold volume up+power buttons together, you will feel 3 short vibrates. That’s all, after it power on your phone, and you will see great performance change.