Q: My husband is currently serving 15 years in prison for Armed Robbery, can the sentense be reduced to 7yrs or maybe 10?

A: It seems here this was a Federal Crime, which means that there were mandatory minimums with the federal court

Pursuant to Rule 35. Correcting or Reducing a Sentence

(1) In General. Upon the government's motion made within one year of sentencing, the court may reduce a sentence if the defendant, after sentencing, provided substantial assistance in investigating or prosecuting another person.

(2) Later Motion. Upon the government's motion made more than one year after sentencing, the court may reduce a sentence if the defendant's substantial assistance involved:

(A) information not known to the defendant until one year or more after sentencing;

(B) information provided by the defendant to the government within one year of sentencing, but which did not become useful to the government until more than one year after sentencing; or

(C) information the usefulness of which could not reasonably have been anticipated by the defendant until more than one year after sentencing and which was promptly provided to the government after its usefulness was reasonably apparent to the defendant.

(3) Evaluating Substantial Assistance. In evaluating whether the defendant has provided substantial assistance, the court may consider the defendant's presentence assistance.

(4) Below Statutory Minimum. When acting under Rule 35(b), the court may reduce the sentence to a level below the minimum sentence established by statute.

So if the case is in federal court all the information provided was already considered in his sentence. Thus, to have an effective chance at reduction he may have to provide assistance to the prosecutor to get a reduced sentence.

I hope this helps