Featured in Call of Duty: World at War, Call of Duty: Black Ops, Call of Duty: Modern Warfare 3, Call of Duty: Black Ops II, Call of Duty: Black Ops Cold War and Call of Duty: Vanguard is a hardcore version of Free-for-All.
Modern Warfare is typically the free version which has a huge map. I wouldn't worry about it personally. That game is a resource hog and RAM usage probably goes up and down quite often. I still use 16g and have no problems running it.