add clang-15 to ubuntu-22 (#8255)

Author: sergei-pyshnoi

images/linux/toolsets/toolset-2204.json

@@ -258,7 +258,8 @@
         "versions": [
             "12",
             "13",
-            "14"
+            "14",
+            "15"
         ],
         "default_version": "14"
     },