Plone 5.1.6 has been soft-released. Please give it a try and let me know if there are any critical issues. https://dist.plone.org/release/5.1.6-pending/versions.cfg
For those who haven't run across soft-releases before, this is the last step before the final release. Because things haven't been finalized yet, some packages may change between now and the release. It is not recommended to use soft-releases in production.
Huge thanks to @mauritsvanrees for prepping the packages for this one.