Hello.
I compiled standard UE’s ThirdPerson project to HTML 5 and started it, opened localhost:8000 in Google Chrome.
Google Chrome process with UE HTML5 game used about 4 GB of RAM. Why? Compiled native version for Win x32 of the game used about 250 MB of RAM. Why HTML 5 version is so resource expensive?
Thank you! 
up up up up
HTML5 unreal engine works with javascript a client background programming language (html and css are not programming languages) also uses web GL as a 3D graphics context which what it does is provide compatibility with multiple operative systems and drivers this will be also known as emulation. Emulation always uses more resources than native programming, unreal engine native windows only uses directx which only works with one os and drivers written specifically for windows.
Google chrome is known for consuming too much ram according to them is because every tab works as a single program and there for the more numbers of tabs you have open the more ram it will consume, you could try with another browsers such as Mozilla, Opera or Edge. Edge could have some awesome features such as native notifications on thw windows desktop so the user could read them later.