On the heels of the release of the second developer beta, Apple has seeded a new public beta build of OS X 10.11.2 to public beta testers. It carries the same build number as the developer release, 15C31f, and is available through the Update section of the Mac App Store.
It's not yet clear what changes OS X 10.11.2 brings along. It's likely that it will focus on bug fixes and performance improvements. With this particular build, Apple asks tester to focus on several key areas, including Mail, Wi-Fi, Spotlight, and USB performance.