The light spill will be visible. Whether you care about it or not is something else again.
Once a movie starts, I tend not to notice ANYTHING except what is going-on within the image. For poor quality DVDs, I can even zoom them-out (make them smaller) such that the image fits inside of my 10' screen and still I can ignore the overspill.
That said, you should at a minimum paint your wall some pleasing darker color (satin or flat) or cover it with a fabric (good for sound too).
In any case these will be relatively cheap fixes if you set-up the system and don't like what you see.