the longer it is the less likely someone watches the whole thing which reduces the view count.
I know more ads can be crammed into longer videos but does youtube look at them any differently?
I’m not sure why but it’s probably ad revenue. Some youtubers have a lot more ad breaks than others. Be that as it may I don’t watch 15 minute videos on a subject that can be covered in 5.
I mainly watch guitar tutorials. Those are usually concise and to the point.