Strange Exit by Parker Peevyhouse

Seventeen-year-old Lake spends her days searching a strange, post-apocalyptic landscape for people who have forgotten one very important thing: this isn’t reality. Everyone she meets is a passenger aboard a ship that’s been orbiting Earth since a nuclear event. The simulation that was supposed to prepare them all for life after the apocalypse has trapped their minds in a shared virtual reality and their bodies in stasis chambers.

No one can get off the ship until all of the passengers are out of the sim, and no one can get out of the sim unless they believe it's a simulation. It's up to Lake to help them remember.

When Lake reveals the truth to a fellow passenger, seventeen-year-old Taren, he joins her mission to find everyone, persuade them that they’ve forgotten reality, and wake them up. But time’s running out before the simulation completely deconstructs, and soon Taren’s deciding who’s worth saving and who must be sacrificed for the greater good. Now, Lake has no choice but to pit herself against Taren in a race to find the secret heart of the sim, where something waits that will either save them or destroy them all.