Update 2.15.13 release notes

Change-Id: Id802a975b1dc75e3b63946d76dd10d420924bc4e
diff --git a/pages/site/releases/2.15.md b/pages/site/releases/2.15.md
index 28a3937..13b81ac 100644
--- a/pages/site/releases/2.15.md
+++ b/pages/site/releases/2.15.md
@@ -424,6 +424,12 @@
 
   The elasticsearch-rest-client is upgraded to 7.0.0.
 
+* Don't abort auto-abandoning if one change failed.
+
+  When failing to query a single change during auto-abandoning, the whole
+  process was aborted. Now the failure is logged and the process continues
+  to attempt to abandon subsequent changes.
+
 * PolyGerrit fixes:
 
   * [Issue 8644](https://bugs.chromium.org/p/gerrit/issues/detail?id=8644):