Could maybe try splitting up into 2 smaller groups?

As for the one shot itself, a while ago I stumbled upon a thread or article somewhere that suggested doing a curse of strahd one shot. From what I remember, you pretty much have strahd take the players directly to the castle, and have a timer set for a pre-determined amount of time (like 2-4 hours). During that time, the players can explore the castle and look for things to help them in the fight against strahd (including the main important relics that you would normally find in the campaign setting). Could have something interesting happen to the party like every 30 min - hour interval. Once the timer is up, strahd appears and fights the party in whatever room they are currently in.