Game crashes while optimizing world, probably due to a memory leak. As the world gets optimized, process heaps keeps on growing until JVM runs out of memory.

This is just to highlight a possible memory leak. Allocating more memory has its limits, world size doesn't (virtually). People with huge worlds (5+ GB) wouldn't be able to optimize them because the memory required would get ridiculous. I was able to convert my world by allocating 4 GB to the JVM (3 still wasn't enough).