Keyboard Mapping question?

I’m looking to change the the key binding used for line sorting from F5 to F15.

I’ve changed config.json to:

packagesWithKeymapsDisabled: [
telemetryConsent: “no”
themes: [
softWrap: true
userId: “bdd4578f-b778-484e-9746-fd76b4a2c3a9”
fontSize: 13
showOnStartup: false

and added the following to the top of keymap.cson:

‘f15’: ‘sort-lines:sort’# Your keymap

But no matter what I do the F15 is being ignored. Any tips on what I’m missing would be appreciated.