lol im pretty sure you don't/can't fret those things with one hand.. also i thought i had seen that these particular tennessee basses arent even actually playable? maybe im wrong lol, but i wouldnt be surprised, the string spacing doesnt even look even!
with that said, i dunno that there's a "limit", if somebody comes along and makes that bass sound good on a song, or as a solo artist, then more power to them. it's not MY cup of tea, but i think it's just as "closed-minded" to knock a 15-string as it is to knock a 5 or 6