I wouldn’t tell him, it was sixteen years ago, you have grown and changed and are a different person, certainly not recognisable to any men who knew you then. Which is where I would feel the need to disclose, if perhaps you knew that a colleague of his was an ex client (sorry I don’t know the right terms).
I’m so sorry that you were ever in this position! You did what you had to do to survive. You have a new life now, a fiancé that you love and two beautiful children. You know your fiancé, would this be a deal breaker for him? Would telling him your past make him see you differently? Are you concerned that someone knows and might use it against you or tell your fiancé?
You don’t owe your fiancé your past, you are who you are, your previous sexual history is not something that he needs to know. Unless it is likely to come up for some medical reason- which is clearly not the case given that you have already had two children with him.
If however, you feel uncomfortable keeping your past from him and this is likely to eat away at you, then it’s completely up to you what you do. You have nothing to be ashamed of, you were very young, very vulnerable and did what you had to do to survive! If your fiancé loves you, then I am sure he would understand! If he doesn’t and holds it against you, then like others have said, he doesn’t deserve you.