I understand that your father has speed issues in China. First, it's necessary to determine if you experience the same behavior using a remote connection outside your house but not in China. We need to make sure if the trouble only occurs in China because of a bandwidth restriction/limitation. Is he located in a regular network (like a house) or is he using a hotel or a private network?
If this streaming issue happens in any remote location, I recommend to assign a static IP to the Slingbox on the router and run the Setup at slingbox.com for Internet Viewing.