Version 2.12.0-259.15.beta

* Cherry-pick 1e114a88d069d2bd7101ad3f5f68e4bd4612bc17 to beta
diff --git a/tools/VERSION b/tools/VERSION
index 325a6a0..e0c8ab4 100644
--- a/tools/VERSION
+++ b/tools/VERSION
@@ -28,4 +28,4 @@
 MINOR 12
 PATCH 0
 PRERELEASE 259
-PRERELEASE_PATCH 14
\ No newline at end of file
+PRERELEASE_PATCH 15
\ No newline at end of file