I haven't used Android L yet so I don't know how fast this is, but this gallery app on Android is fastest there is right now, out of all galleries, stock or otherwise. It's also a tiny app. I don't know how that guy does it. It used to be several times faster on my old Gingerbread phone than the stock gallery app. It's still quite a bit faster on than stock gallery on 4.4. So I hope this is at least as fast as that.
https://play.google.com/store/apps/details?id=com.alensw.Pic...