Firmware build version 23.2.A.1.62 saw a limited roll out across select regions and carriers for the Xperia Z3 series around a month ago. Now the same build number is hitting the Xperia Z2 (D6503 variant only). The update is currently hitting T-Mobile across a number of different European countries including Austria, Germany and Netherlands. Whilst we haven’t seen an official changelog for this version, it is rumoured to add VoLTE. We do not expect this firmware build to roll globally.
Update: The firmware build is also live for the Xperia Z2 Tablet LTE (SGP521) across the same carriers/regions.
Thanks Aaron and Maurício!