Your computer isn't powerful enough
More of a driver issue here, Nouveau struggles with Shaders and high polygons count.
But it's possible the proprietary driver does not fare much better yeah...
Seriously devs, tweak your damn shaders so they don't eat all of my memor(ies).
I tried Unigine Valley and here are the results :
AMD Ryzen 5 1500X
Gigabyte Geforce 780 Windstorm 3X
Min FPS : 14.8 (was a stutter)
Max FPS : 116.6
Average FPS : 65.0
Points : 2718
Will try crysis when i can.