Lenovo's new Lollipop OTA update bears a build number K920_S226_150429_ROW for Vibe Z2 Pro. The firmware comes in at a considerable 1.23GB in size, so it is recommended that you download it over a stable Wi-Fi network.
Following the installation, the Vibe Z2 Pro gets spruced up with Material Design elements throughout the UI. Most importantly, the brand new ART runtime ensures that every task you perform on the device feels snappier than before.
Thanks for the tip, Ankur!