It would be very rare for an audit to go back 18 years ago. If by the slim chance they did, you would pay tax on the $1500 plus interest and penalty. If you had losses against that $1500, you can subtract them from the amount received. That would be tough to prove unless you kept a loss and win sheet from that many years ago.
My guess is this will not be an issue. Don't bring it up at your audit unless they actually do.
