Android 5.1 Lollipop is expected to be a rather large update, returning the silent mode missing from Android 5.0, improving system stability, RAM management and battery management, and fixing sudden app closures, Wi-Fi problems and sound problems.
http://www.pcadvisor.co.uk/features/google-android/3514191/android-5.0-lollipop-release-date-new-features-upgrades-android-5.1/