Seeing the same thing - there seems to be some leak in UnrealLauncher. System with 16GB RAM was at 100% commit charge after being left overnight, with low VM warning. Event log showed:
Windows successfully diagnosed a low virtual memory condition. The following programs consumed the most virtual memory: UnrealEngineLauncher.exe (3240) consumed 523390976 bytes, avp.exe (2072) consumed 376832000 bytes, and chrome.exe (10180) consumed 285159424 bytes.
Closing UnrealLauncher immediately took commit charge down from 100% down to only a few %.
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LogInit: Version: 4.5.0-2282482+++depot+UE4-LauncherReleases
LogInit: API Version: 2282482
LogInit: Compiled (64-bit): Sep 3 2014 00:32:02
LogInit: Compiled with Visual C++: 18.00.21005.01
LogInit: Build Configuration: Shipping
LogInit: Branch Name: ++depot+UE4-LauncherReleases
LogInit: Command line: “C:\Program Files\Unreal Engine\Launcher\Engine\Binaries\Win64\UnrealEngineLauncher.exe” -SaveToUserDir
LogInit: Base directory: C:/Program Files/Unreal Engine/Launcher/Engine/Binaries/Win64/
LogInit: Rocket: 0