Update 2.15.12 release notes

Change-Id: Ibf61b33524b69f240f8924b106067591327ea5e4
diff --git a/pages/site/releases/2.15.md b/pages/site/releases/2.15.md
index 9af9c0a..fa32f1c 100644
--- a/pages/site/releases/2.15.md
+++ b/pages/site/releases/2.15.md
@@ -389,7 +389,7 @@
 
 * Update Jetty to 9.3.18.v20170406 (updated to 9.3.24.v20180605 in 2.15.7)
 
-* Update JGit to 4.9.0.201710071750-r (updated to 4.9.8.201812241815-r in 2.15.8)
+* Update JGit to 4.9.0.201710071750-r (updated to 4.9.9.201903122025-r in 2.15.12)
 
 * Update Joda-Time to 2.9.9
 
@@ -407,6 +407,13 @@
 
 ### 2.15.12
 
+* [Issue 10562](https://bugs.chromium.org/p/gerrit/issues/detail?id=10562):
+Upgrade JGit to 4.9.9.201903122025-r to fix corruption of packfile
+list due to concurrent access during GC.
+
+  See [JGit issue 544199](https://bugs.eclipse.org/bugs/show_bug.cgi?id=544199)
+  for details.
+
 * [Issue 10531](https://bugs.chromium.org/p/gerrit/issues/detail?id=10531):
 Fix LocalUsernamesToLowerCase program.