H1Z1 is known to cause memory leaks. which is what you are seeing there right now. its poorly programmed and unoptimized and i dont know if they are still releasing patches for that game.
you can do any of the following to "fix" that for the meantime.
* reinstall the latest chipset driver for your motherboard. BIOS as well if necessary.
* optimize your virtual memory settings in your OS.
https://www.pcworld.com/article/2840886/if-windows-virtual-memory-is-too-low-you-can-increase-it-but-there-are-trade-offs.html
* send memory leak reports to the game support forum and wait for their next bug fix release
* download CleanMem (WiseCleaner or alternative tools) to help your system manage RAM better (temporary fix)
http://www.pcgamer.com/dealing-with-memory-leaks/
https://www.wisecleaner.com/wise-memory-optimizer-user-guide.html
* transfer game files to an SSD (open world games can benefit from this)
* upgrade your RAM to a 2x8Gb