It reminded me about this very simple scene I rendered (around 2009) that took me almost 60 hours to complete:
https://victorribeiro.cgsociety.org/yjoi/my-last-background
1 - https://www.youtube.com/watch?v=mvjKM-iVxYI
Also, I'm not a graphic designer, but I spoke with a developer years ago who mentioned that indoor and outdoor rendering are quite different. Your image is an outdoor scene, but the NVidia video focuses on indoor architecture. (I see that they have a window in their example with some grass, but it's not a very wide space.) Do you think your rendering time would have been cut down back then if you composed a scene similar to what NVidia demoed? Any thoughts on RTX outdoor rendering?
All I know is that with things like Quixel [1] and megascans they can produce really amazing environment scenes (the kind I was trying to achieve with my render) that render in real time.
To be honest, there was a lot of things I could do to improve my scene rendering time, but I wanted to try using grass as real geometry so each blade of grass would interact with every photon of light. I remember the blades of grass being reflective and refractive (although you can't see that in the low quality render, compressed as JPG).