why are you applying for a visa.if,as you say you got into trouble 15 yrs ago and got a criminal conviction,then you will be turned down for the visa. if you only want to visit the USA for less then 3 months,just go on the visa waiver system.
15 years is normally the maximum time that the US will go back for visa purposes - so you would probably get your visa without delay if you were to apply for one.