I think they reduced the number when they did a stage version about 10 years ago.. but if you cut them then you don't get the impact of the dozen dwarves coming to tea (six is not a big deal..) and a dozen is a fairly small party to reclaim the mountain, fewer might be ridiculously quixotic. I suppose that Thorin will be a big name actor, Fili and Kili, Balin, Dori and Bombur will be well known and for the rest it will be the gig of a lifetime for half or dozen or so Kiwi journeyman actors filling up the background. Though if they are looking to save cash they might digitally create them