Is it normal for a febrile seizure to last as long as 15 minutes in a three year old boy? Are there any long term effects to seizures as long as that

It's Probably OK. Febrile seizures are considered "typical" if they are 15 minutes or less in duration and are "all over" body seizures (not just one limb or one half of the body involved). There are no known long-term problems with febrile seizures, even at that length. For otherwise healthy children, it takes quite a while (>30-40 minutes) for any seizure to start to have a significant risk of injury.