So F13-15 on my keyboard are detected by input-remapper:

I can use input-remapper to assign them as duplicates of existing shortcuts. However if I open the COSMIC shortcuts binding box and press those keys, they don't appear in the box. I wonder if this relates to #1659 and F12-16 don't appear in selected keyboard layout.
I've tired manually adding F15 as 'key' by editing ~/.config/cosmic/com.system76.CosmicSettings.Shortcuts/v1/custom but that doesn't seem to get round the issue.
So F13-15 on my keyboard are detected by input-remapper:

I can use input-remapper to assign them as duplicates of existing shortcuts. However if I open the COSMIC shortcuts binding box and press those keys, they don't appear in the box. I wonder if this relates to #1659 and F12-16 don't appear in selected keyboard layout.
I've tired manually adding F15 as 'key' by editing
~/.config/cosmic/com.system76.CosmicSettings.Shortcuts/v1/custombut that doesn't seem to get round the issue.