Nah, it's a systemd setting. You need to edit /etc/systemd/logind.conf and change HandleLidSwitch= to HandleLidSwitch=suspend-then-hibernate, and the create or edit /etc/systemd/sleep.conf to change the timeout value:
[Sleep]
HibernateDelaySec=900
With the above, the system will automatically hibernate after 15 minutes of sleep.
Note that if you're using a full-fledged DE or a third-party power profile manager, you may need to disable any lid-close actions in there (if it doesn't have the suspend-then-hibernate option) so that systemd can handle it properly.