Well, I like to take it slow (and stealth as much as I can, no running around guns blazing, I need to conserve resources) and it took me 14 hours (with some AFKing, dunno whether the timer ticks when on pause) on the first run (on Hardcore), which I ended only missing 2 files, 1 goat, 1 hidden treasure, 1 piece of the necklace and the Vârcolac Alfa IIRC, maybe another of those multi-piece treasures or something minor I can't remember. I haven't tried Village of Shadow yet, did a second Hardcore run first, and I never use the infinite ammo "cheats" you can get for CPs, so I'd wager it'll take longer, but not by much (sure it's supposedly going to be more difficult, but I already remember most of what I have to do and I have some good weapons upgraded and the recipes done, so that'll factor in). It definitely doesn't feel like a 20 hour game, not to a RE veteran and not on lower difficulties at least, but who knows, maybe Village of Shadows will prove me wrong.
That being said I'm not complaining, game length doesn't equal quality to me, I really liked the two runs and I can easily see myself doing a lot more once I cool off and forget about some stuff (the second run was less enjoyable because I did it immediately after the first one and I remembered almost everything, including some of the "jump-scare" mob spawn locations - getting that last goat was very satisfying though). Hopefully some good DLC (not the multiplayer BS, I couldn't care less in a RE game) will be released.