Sony has rolled out another firmware update for Xperia M2 (D2303, D2306) & Xperia M2 Aqua (D2403, D2406). So this will replace the previous firmware with the build number 18.3.1.C.1.16 from the new build number 18.3.1.C.1.17. The Update is live on some regions. This will be rolled out to other regions shortly.
We can expect only Bug fixex and performance enhancements in this firmware update as it is a Minor Update. Also we can guess this should be the last update for Xperia M2 & Xperia M2 Aqua before getting Android 5.1 Lollipop