Your chances are as high as anyone else. Your ISP can figure it out and report you or you'll be found out another way. It's hard to say what your chances are. If you're worried, don't do it.
Completely depends on the torrent you are downloading.
Using torrents to download a new movie that just came out in theaters -> illegal
Using torrents to download something free like Ubuntu or non copyright material -> legal
As for chances getting caught downloading copyright material, I have no idea but I'd imagine they're pretty low but it really depends on what, how and quantity you are torrenting.