Human Head, developer of Prey 2 has said that the single player campaign will last 15 hours (average), if and only if they decide to skip exploration and side quests.
In an interview to Eurogamer, Chris Reinhart project lead said, “We’re focused on making it a strong, powerful single-player experience,”
“And we’re tied with Bethesda, which has proven they are the masters of making awesome single-player experiences. It’s an interesting challenge. It makes us change some of the other things we do. The single-player game has to be larger. There’s more player choice. There’s more to do.
“We’re targeting, for the average player, at least around 15 hours to play through. But because there are so many open world activities you can do when you explore around and find different things, it’s hard to put an upper cap on it.
“I guess if someone were to haul ass, they might be able to get through it under that. But I could haul ass through many open world games and get through them in a handful of hours.”