Sony has started rolling out a new update to its Xperia Z5 family of devices that bumps the build number to 32.2.A.0.305. Sadly, nothing else is currently known about the update including what it brings along, although it's expected that the latest Android security patch will be there. As is usually the case with OTA roll-outs, it may take sometime for the update to hit your device. Meanwhile, if you feel impatient, you can manually check for the update by heading to your handset's Settings menu. Via
Source: http://www.gsmarena.com/sony_xperia_z5_series_receiving_a_new_update-news-20937.php