Conversion is not designed to minimize memory usage, it's designed to be as flexible and powerful as possible. Since each conversion runs in it's own process and the process is killed after the conversion completes, the only way that memory consumption can cause a crash is if the memory consumption of a single conversion is larger than the amount of RAM + swap on your machine. I find that highly unlikely.
Given that your windows is blue screening, which should never happen with a conversion (conversion is a user space process), I would suspect you have hardware issues, most likely something breaks under heavy load.
That said, if you have an epub that consistently causes a crash every time you try to convert it, open a ticket and attach it and the conversion logs.