Bug 1148522 - Increase GIP f to 15 chunks r=me a=config-only

--HG--
extra : rebase_source : bf9cf00d1b1fc736404dbdefbd1de17f0a495da4

testing/taskcluster/tasks/tests/b2g_gaia_ui_test_functional.yml

@@ -34,7 +34,7 @@ task:
 
   extra:
     chunks:
-      total: 3
+      total: 15
     treeherderEnv:
       - production
       - staging