Sony Mobile may have just certified Android 5.1 Lollipop for the Xperia Z3 and Xperia Z3 Compact judging by new listings. Firmware build 23.2.A.0.278 has been certified by the PTCRB for the Xperia Z3 (D6653) and Xperia Z3 Compact (D5833). Given the move from build format ‘23.0’ for Android 4.4.4 KitKat to ‘23.1’ for Android 5.0.2 Lollipop, there is a strong likelihood that ‘23.2’ will be Android 5.1 Lollipop.
Update: There is the possibility that this is not Android 5.1 after all, judging by this handset detection listing. (Thanks Aaron!)
Thanks to all that sent this in!