2.15.3 is about to be released (https://gerrit-review.googlesource.com/c/gerrit/+/185671)
Bug fixes that are important are:
* "Fix file handle leak when running GC."
** This could cause gerrit to fail one day without warning without this fix.
* Allows project admins to set a change as WIP or mark a change as ready for review.
** Currently only admins can do this. With 2.15.3 project owners can now do this. This will partially resolve. T197238 even though the button was there. Only admins were able to help.
* Alot of fixes for internal errors.
278 commits since 2.15.2 (https://github.com/GerritCodeReview/gerrit/compare/v2.15.2...stable-2.15)
Elasticsearch 5 and 6 are now supported but not yet recommended for production use yet.
See release notes at https://gerrit.googlesource.com/homepage/+/md-pages/releases/2.15.md#2.15.3