[2019] graphic card change

If you now have a severe FPS drop make sure your discrete GPU is being utilized and not an onboard GPU (primarily laptop users).
From NVIDIA Control Panel:
3D Settings-> Manage 3D Settings
Tab "Global setttings"
Preferred Graphics Processor
Select: High performance NVIDIA processor

Another option to try if the above doesn't work: Documents > My Games > Rainbow 6 Siege > GameSettings.ini > Change "GPUAdapter=0" to "GPUAdapter=1"