Update charts for voltha-2.15 release

Signed-off-by: Eric Ball <eball@linuxfoundation.org>
Change-Id: I3b22a71f03965f800ba37e998535caac4da838b1
diff --git a/voltha/Chart.yaml b/voltha/Chart.yaml
index f4df7fa..5bc3b01 100644
--- a/voltha/Chart.yaml
+++ b/voltha/Chart.yaml
@@ -1,4 +1,4 @@
-# Copyright 2019-2025 Open Networking Foundation (ONF) and the ONF Contributors
+# Copyright 2019-2026 Open Networking Foundation (ONF) and the ONF Contributors
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -17,7 +17,7 @@
 
 ## Chart version for package 'voltha'
 ##   Increment when Chart.yaml changes
-version: "2.15.4"
+version: "2.15.6"
 
 description: "A Helm chart for Voltha based on K8S resources in Voltha project"
 keywords:
@@ -36,6 +36,6 @@
     url: "https://www.opennetworking.org"
 
 # appVersion refers to release version of voltha-go
-appVersion: "3.7.4"
+appVersion: "3.7.13"
 
 # [EOF]