Which one will have more playtime, Mad Max or MGS V: The Phantom Pain?

MGS does seem like fun, I've always liked stealth games. But I also like post-apocalyptic themes, and while I don't play many vehicle/melee combat games, Mad Max interests me as well. They seem pretty much equally good, I'm just worried that I'll buy one of them at full price and it feels too short.

10€ isn't a big difference. But yeah, it's a good point that I might feel different about FO4 if I've played another post-apocalyptic game to full/near full completion right before it.

I'm just not so interested in fantasy anymore.

A sandbox quite literally. And well, I've played some of the MGS games, and watched playthroughs of the rest. Did you say that because it's kinda necessary to have played the previous games to understand the story?