Build owners plugin on Gerrit v2.15

Change-Id: I73d67006f00215bfc8da94f7f845c0e59eb0ad07
diff --git a/jenkins/gerrit-buck-bazel-plugin-owners.yaml b/jenkins/gerrit-buck-bazel-plugin-owners.yaml
index ff1c0ac..d8c71f4 100644
--- a/jenkins/gerrit-buck-bazel-plugin-owners.yaml
+++ b/jenkins/gerrit-buck-bazel-plugin-owners.yaml
@@ -54,4 +54,5 @@
           targets: 'plugins/owners plugins/owners-autoassign'
           branch:
             - master
+            - stable-2.15
             - stable-2.14