It looks like the Stamina Mode finally returns to the Sony Xperia Z5 family of devices. As we can remember, this function has been removed by the Android 6.0 Marshmallow update.
The build number changes to 32.A.0.224. The android number changes to 6.0.1. Stamina Mode is Sony's own interpretation of a low power using state.
It can take a couple of weeks before the update kicks in, so you have to be patient.