It's more like, how long would it take you to find 2016 blocks of the current high difficulty on pen an paper?

Then there's the first difficulty adjustment, down by maximum a factor of 4.

And again, how long would it take to find 2016 blocks of this still damn high difficulty.

Then there's the second difficulty adjustment, down by maximum a factor of 4.

There will be many adjustments before it's back down to genesis difficulty, but it would take decades, centuries?