To launch DOOM 2016 release of the game you need 8 GB of RAM, but the game can run on 4GB.
For this game you need to remove the restriction on the amount of RAM. This can be done with a special pomoschtyu updates.
Download here Doom Doom 4RAM update fix.
Installation takes place automatically if the update does not find a folder with the established of DOOM, do it during the installation process.