Update 2.15.12 release notes

Change-Id: I95260d9bf48e68ee630a25099021d9cc5e92ac28
diff --git a/pages/site/releases/2.15.md b/pages/site/releases/2.15.md
index 3c913df..9af9c0a 100644
--- a/pages/site/releases/2.15.md
+++ b/pages/site/releases/2.15.md
@@ -427,6 +427,9 @@
 * [Issue 10568](https://bugs.chromium.org/p/gerrit/issues/detail?id=10568):
 Add `is:submittable` to search suggestions.
 
+* [Issue 10587](https://bugs.chromium.org/p/gerrit/issues/detail?id=10587):
+Fix setting group visibility in PolyGerrit.
+
 ### 2.15.11
 
 * [Issue 10106](https://bugs.chromium.org/p/gerrit/issues/detail?id=10106):