you were also sold a clown loach even though you only have a 15 gallon tank. you should have at least a 75 gallon tank if not bigger for that fish.
here is a link for some info on the fish. most places will sell whatever they can to keep money flowing in. whatever looks good and dazzles uninformed ppl. i too had some clown loaches for a while in my 40gal and learned my lesson to research the fish i see at the lfs before i buy.