Wow! Your daughter's boyfriend must be from a really liberal JW family! Normally, that would never, ever, in a million years be allowed. Have they celebrated any holidays together? Valentine's Day?
Either that kid comes from a real liberal family or he's living a double life and is desperate to get out.
I wouldn't assume you need to become overly concerned yet. Do you know how he feels about being a JW? Is he baptized? Does he want to remain one when he becomes an adult? If he wants out, you could be his saving grace of giving him a way to experience normal things in life ... like having a "girlfriend" when you're 15.