Well the threas sais it.. with vanilla it runs but since the new launcher is there Optifine crashes when Java OpenJDK 15.0.2.7 is used I hope optfine can fix this ...
FPS drops start right after any world loads and RAM usage doesn't even go under 4.2GB(if i remember correctly) in any world. If i give more ram to the game RAM usage just goes up and up and up and up.