Game require a good graphics cards that can manage Lumens and other stuff. Issue is old graphics cards will struggle, mostly due to LUMEN lightning.

IF settings everything to LOW isn't enough, here's a step by step to gain FPS:

• First, set your settings to LOW. Everything.
  
• Then, close the game and go to \AppData\Local\LevelZero\Saved\Config\WindowsClient
  
• Then, edit the GameUserSettings.ini file (you can make a copy beforehand)

Then, edit the following values:

• AOLevel=0
  
• sg.GlobalIlluminationQuality=0
  
• sg.ReflectionQuality=0
  
• sg.PostProcessQuality=0
  
• sg.LandscapeQuality=0

Save, relaunch the game and see for yourself if it helps.

You will loose some lightning compared with Lumen ON. Play accordingly ;)



Thanks to MouseKing for helping me testing and tweaking this guide.