Sony starts rolling out March Android Security patch to its Xperia Z5, Z4 Tablet, and Z3+. The update comes with the software build number 32.3.A.2.33. Moreover, in January all these devices gets the Nougat Update.
Coming back to the Security Update, It weighs around 187 MB in size which includes the monthly security patch. It also fixes the audio issues that were introduced with the Nougat update. Security Patch consists of some fixes for the latest Bugs which were found in the Android.
As this is an OTA update, It will take some time to reach you. If the notification did not reach you don’t panic it will in couple of days. Meanwhile you can check it manually going through the Settings>>About Phone>>software update.