I am not sure if this helps you because for me, the game didn't crash upon entering dialogue but during the fights, but maybe it is worth a shot. The considerable lag and the crashes in the place seem to be connected to the amount of invisible enemies and cursed items. Getting rid of those in small groups made the whole place more stable. You can find them with Volo's eye or an Elixir of See Invisibility, the cursed items can be either decursed or just smashed. The servants' staircase seems to have it especially bad.
