A minor update has been certified by the PTCRB for the Xperia M2 (D230X). The update is a marginal one and would move the build number from 18.3.1.C.1.15 to version 18.3.1.C.1.16. This may be the last Android 4.4.4 KitKat update, before Sony updates the Xperia M2 to Android 5.1 Lollipop later in the year.
Xperia M2 firmware build number 18.3.1.C.1.16 certified for D2303, D2306 variants
Thanks Sergio!