Can a person obtain a SECRET clearance if they used controlled substances for a period of time when they had a SECRET clearance a number of years earlier, but have not had an incident for a period of over 15 years? ???
The clearance only usually goes back 7-10 years in your life.
15 years is a long time in the past and hopefully you learned from your mistake and the mistake was only a little one and not one in which you actually used drugs over a long period of time or actually used some of the harder drugs.
Seems like the question on your drug use 15 years ago probably wont' be asked.