Sleep/hibernate after pre-selected idle time period

[Alex]

Hi,

I have a fedora30 desktop that's used infrequently throughout the day.
I'd like it to go to sleep on its own after 15 minutes of inactivity.
How can I do this?

The install was done using defaults, so I'm using GNOME with its
default applications and configuration.

An option to configure this from the command-line would be
appreciated, although I can also use the GUI.

Thanks,
Alex