ah ,the good ol' castrum and prae ^^;
Nothing can really be done here. Both of these dungeons are now at the point where 4 man teams could pass through them. We're overgeared and people now know it by heart. The roulette is why people still do it at all, but the issue is, many have done it 100's maybe 1000's of times now. The dungeons cutscene's are long and numerous, as well as spreading out THROUGH the dungeon as you go. SE learned from this mistake and no longer place long cutscene's inside of the dungeon itself (as you noticed, you were watching 5-10 min cutscenes for those dungeons if you were watching them all the way through. If you rush things, you can get through the dungeon in 20 or so minutes. If you watch the cutscenes... the dungeon quickly becomes an hour long journey, in which most of the party will simply be sitting there.... doing nothing.

By no means is it a good situation and it still causes quite a toxic environment for newcomers who just reached it. I try to be more courteous to the newcomer's whenever I do it, but as I said, it can easily be passed by 4 man teams. So 1 or 2 people will not curb the rest. But I usually try to warn new players to either sit back and enjoy the cutscenes, or to skip them, learn the dungeon by running along with us, and rewatch it later. There's a few things you need to know, but it's mostly just where to go and what to click. You can pretty much just run through everything and beat down anything that comes near you fairly easily.