Before you read this I apologize if there are grammar or spelling mistakes as English is not my first language.
I really like the realms of Minecraft as it provides unique maps we can play.
Im suggesting a different world format being used on the server side which can improve server side performance even way faster.
Hypixel, a world famous minecraft server has a skyblock server which uses slime world format in which they individually save the players world and load them only when they join. Whats amazing about this is that they can handle tens of thousands of players real time without hassle.
If realms were to use similar world format, the world size will decrease and it will be beneficial in the long run considering new updates.
So to conclude, realms should try incorporating slime world format developed by Hypixel team to reduce disk usage and improve performance.