a technique I've used to remove tiles relatively quickly is to use the claws on back of a hammer. angle the wedges on the claws against the wall on a clear stretch where there are no tiles and slide the hammer along hard so the claws hit the side of the tile. if you do it hard enough, much of the tile should pop off. I've found this much faster than using scrapers, steel rules, etc. but it is quite tiring as you have to hit the side of the tile pretty hard. be sure to protect your eyes, hands and arms from flying tile fragments. and of course this is no good if you want the tiles to come away intact.
