I think you can guess the next 4. XD I could probably design another 5 sometime in the next six years
Just reset the chevrons back to bronze and one, but put a little bronze star left center below the chevrons. Changing the colors of the stars from Bronze, Silver, Gold will allow 3 more full passes of each set of chevrons. So Gold star and 5 gold chevrons is 60 years. EDIT: Like this, but with better paint skills; https://imgur.com/a/VvpPwmf
Military does like to add ornaments to ribbons, maybe instead of a star I could create a 3d model for the skjaldborg emblem in bronze silver and gold and 'pin' it to the ribbon. Each grade would equal 15 years, and you could earn up to three meaning your maximum service time would be 195 years. XD