High RAM usage then it will hang

After i load/play my main world, it will consume all of my RAM then it will eventually hang. (picture with 96~99% RAM usage)

However, if i play other map (which was not a copy my main world) or created new world, the RAM usage is normal and it will load/generate world instantly (picture with 41% RAM usage).

 

Kindly resolve this since the affected world is my main world.