Aware of the giants Shostakovich and Beethoven who both wrote 15 string quartets (unless you count the Grosse Fuge separately), I chickened out and wrote a rather short work in one movement for my 15th. Most of it is based on the theme heard right at the outset and the scherzo section returns to conclude the work, albeit in a somewhat anarchic form. For anyone interested, it can be heard here
https://play.reelcrafter.com/dko22/latestworks