It’s not too big of a patch (nothing compared to Dead Rising 3’s 13GB update), and you need to have a good internet connection to be playing Titanfall anyway, so it shouldn’t delay you getting into the game for too long.
If you’re buying the game digitally, the patch will be included in the initial download.
Yesterday, Respawn co-founder Vince Zampella said that if you’re lucky enough to get your hands on a copy of Titanfall before its official release date, you can go ahead and play, as Respawn will not “stop or ban legit copies.”