My husband was just brought in for questioning some lady said he sexually assaulted her 15 yrs ago can he go to jail?

Where was it (country, state), and how old was she at the time?

If the police did not feel there was someway they could still charge him or arrest him I don't see why they would take him him to question.

He should not say a word without an attorney

As Chuck said, if there wasn't a chance of prosecuting, they wouldn't be bringing him in. On the other hand, proving a 15 yr assault charge will be difficult.

I agree he should say nothing without an attorney.