I presume in BOS you're leaving from Terminal E with all the international flights. The airberlin web site blew up when I tried to search for flights so I don't know what time you're leaving. It gets a bit crowded in the terminal for the evening TATL departures, 6 PM on. But I've never seen things run really slow there and usually it is pretty efficient. Of course Airberlin could have a single check in spot open and a long line of pax to check bags. But if I were you, I would not worry.