If it's one time promotion, it will expire after 139 hours, or almost 6 days. So, if he will lock tokens for 15 days, later he won't be able to lock it for 360 days because this promotion will expire until it. Unless Freebitco.in will offer it again after some time.
That's what I thought too at first, but I think it's just the 45% APY on 15 days that is a one time promo. The opportunity to earn interest on FUN will still exist on freebitco.in, just not that specific interest rate.