Just yesterday, Google announced the security update for March 2016 was live and heading out to the Nexus family of devices (BlackBerry is already rolling it out to the PRIV), they also posted the factory images for these devices and posted their security bulletin showing us what exactly was fixed in this new update. While these updates are primarily for fixing vulnerabilities that are found in the software, it's also a good opportunity for Google to roll out fixes to improve performance and stability as well as bugs. That's exactly what they are doing with the Nexus 5X's March update.
Not only does the March security update include a slew of vulnerability fixes, but it also includes a few performance and stability fixes, at least according to reddit user GoogleNexusCM. The user did not mention specifically what bug fixes and other fixes were in this update for the Nexus 5X, but users of the Nexus 5X should see a big difference after getting the OTA which is supposedly beginning to go out as early as today. Those of you wanting to flash the factory image, it'll be build MHC19J, as there are two builds available on the developers site. Updates for the other Nexus devices should be rolling out shortly as well. Remember that with these OTA's they do take some time to roll out completely. They start by rolling out the update to a small percentage of users, to be sure that they are able to update their device and get back online without any issues. After a week or so, the majority of users will start to get their update.
Google has kept true to their word of pushing out a security update each and every month. Luckily for Google, the majority of their devices are not carrier devices (with the exception of some Nexus 6 models), so they are able to push out the updates much faster. An issue that Samsung and HTC are running into with their security updates for their flagship smartphones. A number of Verizon phones are still on the November or December 2015 security patch, even though we are in March 2016.