hey ngnjx, you can find info on this here: https://docs.decentraland.org/player/general/meet-with-friends/

In general only 100 people can be visible in the same "island". However a lot more people can join a realm. We hope with the new client the performance will be much better with more players being in the same scene as well. If you need help with the event, you can also send an email to the Marketing team at marketing@decentraland.org