This group is used to override CriticalMonitor targetted to Exchange 2015 HelathSets. Member healthsets will generate critical alerts and will have error unhealthy states.
<ClassType ID="Microsoft.Exchange.15.Custom.CriticalHealthSets.Group" Accessibility="Public" Abstract="false" Base="MSIL!Microsoft.SystemCenter.InstanceGroup" Hosted="false" Singleton="true" Extension="false"/>