I finished DOOM (2016) in 8.8 hours. Granted I didn't stop for collectables and was on normal mode. I tried Eternal but got bored after 2 hours so that's what I'm basing it off.
My steam friends currently have about 17 hours (they bought it early) but they like collecting stuff and getting 100% achievements. I'm not sure how long the story is without 100%ing it but it shouldn't be too different from the other games.