'openParentApplication(_:reply:)' has been explicitly marked unavailable here - Xcode 7 Beta
+[WKInterfaceController openParentApplication:] is only relevant for WatchKit1 app extensions because with WatchKit1 app extensions, the appex is running on the phone instead of on the watch.
With WatchKit2 app extensions, the appex is running on the watch, so actions such as this are less trivial to accomplish. You probably want to use -[WCSession sendMessageData:replyHandler:errorHandler:] from WatchConnectivity.framework for what you're doing.