Without an open listening port you will not receive any peer initiated requests. The only way you can connect to a peer is if you initiate the connection and most peers in a swarm already have the connections they need.
As new peers enter the Swarm they will try to connect with others except they cannot reach you. You will not know they exist until you receive a Tracker update and by then they may have all the peers they need. If you cannot receive incoming connections your performance is going to be horrible on most torrents. I highly recommend you get a better internet connection and mobile broadband is never a good option when using peer-to-peer downloading.
Fiber optic is usually the best option