It appears that Sony will release Android 5.0 Lollipop update for its Xperia devices during 2015. However, now you can give a feel of Android 5.0 Lollipop on your Xperia phones running on android 4.4.2 and later with Android 5.0 Lollipop Theme. The theme will also works on Android 4.3 Xperia phones, but it requires root access on your phone.
Android 5.0 Lollipop has a dramatic new look dubbed Material Design. The Android 5.0 Lollipop theme for Xperia phones by an XDA member JanM RS will bring the official material design wallpaper, Navigation keys, lock screen, home screen and more to your Xperia devices.
Installing Android 5.0 Lollipop theme on your Xperia phones running on android 4.4.2+ is simple. Download [HERE] the theme and install it like any APK file (no root requires). For Android 4.3 running phones, the theme requires root access and superuser mod to work.
Once installed, apply the theme. To do so, long press in Xperia Home -> Themes -> choose Android 5.0 Lollipop theme and press “apply”. Or, go to Settings -> Personalization -> Xperia Themes -> choose Android 5.0 Lollipop theme and press “apply”. (source – XDA)