Upgrade bazlets to latest stable-2.15 to build with 2.15.9 API
Upgrade bazlets to latest stable-2.15 to build with 2.15.9 API

Change-Id: I4b4d97b11c7c45dc40c7ba006619f5430c79b26a

GerritCodeReview/plugins_quota,GerritCodeReview/plugins_quota,GerritCodeReview/plugins_quota