This was the bench-mark pattern. The '15' represented fifteen strings in two diatonic octaves and the '4' indicated four pre-tuned chords arranged to allow for playing in the keys of C major and D minor. A "Proper Young Lady" could extract a variety of tunes from this instrument!.
This example came from a previous life as Still Art in the John McCrady Art School in New Orleans. Its life before that time is unrecorded.