Assuming that we have the knowledge we have now? So all the text books and paper libraries survive? No infrastructure just knowledge and people power? I'd give it 100 years max before we ruin it all again.
Just looking at the picture you selected, why change anythin.g
Because you and your capitalist buddies can't make money on trees and lakes, you need to exploit people and resources or you can't enjoy life. God forbid you would need to share your space with a human from another mountainside, or worse yet what if you work harder than they do and they still get to eat. The horror!
Oh Yeah ----
Well yer a pinko commie, so there!
Yes! Yes I am!
We would start with considerable knowledge.
It would take a substantial amount of time to recover. Remember first we'd have to re-learn to survive and adapt without technology. Then if we failed to pass on specific knowledge and instruction to future generations technologies we once had could be lost forever. I'd say it would set humanity back at least 1000 years if not 2000 years.