I've contacted Mahjong prefab original author, and got him to release Manual Synced beta. It means, you can have reasonably big amount of mahjong tables in one world, without networking lag (bots playing will still ruin your day). So, to show this off, I've made a world with 12 tables. Yes, 48 mahjong players playing side by side, if you ever need a BIG mahjong meetup.

I can't release more worlds this week so, here's a link:
https://vrchat.com/home/world/wrld_6b331554-5d00-4e49-abc0-2f79ddacdf9f

Maybe through all these "Haha more tables pls" jokes I've managed to make something usefull for bigger weekend mahjong meetups.

There is a catch, every additional mahjong table will increase the time in "Initializing World" 
and there is a hard time limit before it kicks you out
12 tables should be doable for anyone who has VR capable PC though.

Original author called this modification a "beta" so there might be some synchronisation issues, but as far as I can see, it just works. And it feels slightly more responsive than in normal worlds with 4 tables.

Test it and maybe it's the future, because I've seen too many late night weekend mahjong instances with at least 30 people, when only 16 can play...