My upgrades take +/- 12 days!
I'm pretty sure coc and bb had similar upgrade time too
and all other Civilizations games.
If you want fast upgrades, well... There's always simcity
I kid. But as we advance, time and workers are always the hardest part, not the rss. Which is why we are saving speedups for event discount or crucial upgrades. As for me, upgrading airstrip, war academy, mercenary camp and fort will at least take 12 days. I do world wars, and without them literally no wars for me
so I crown them (at least airstrip and war academy)