http://breezewiki.catsarchywsyuss6jdxlypsw5dc7owd5u5tr6bujxb7o6xw2hipqehyd.onion/minecraft/wiki/Java_Edition_1.14
Optimizations Inside the optimize world screen there is now an option to remove cached world data (e.g., height maps and light), so that it is re-computed when the world is next loaded. Optimized nether portals. They will now keep the other side loaded for 15 seconds after an entity goes through.