A new plugin was created upstream to support renaming projects. See https://gerrit.googlesource.com/plugins/rename-project/
2.15 support is being added in https://gerrit-review.googlesource.com/c/plugins/rename-project/+/192750
git clone https://gerrit.googlesource.com/plugins/rename-project
Build instructions: https://gerrit.googlesource.com/plugins/rename-project/+/refs/heads/stable-3.2/src/main/resources/Documentation/build.md
Some instruction as to how we build Gerrit https://wikitech.wikimedia.org/wiki/Gerrit#Build_Gerrit