The firmware version of the Zenfone Max Pro M2 March Update is 15.2016.1902.192. According to the release notes, there are a few other fixes included as well.
ASUS' press note says that the Touch firmware has been upgraded on the ZenFone Max Pro M2. The front camera quality has been improved. The third major improvement seems to be for the status bar's display.
The Zenfone Max Pro M2 March Update is being released in batches, and should be rolled out to all devices soon.
ASUS Zenfone Max Pro M2 March Update Download
If you want to download the update right now, you can do so from the official Help Desk page. This is a full system image, which is about 1.89GB in size.
It is worth mentioning that this update is for the stable version, not the Android Pie Beta which was launched a month ago.