+111111

I don't believe a manager can be effective at 15 direct reports. I think it's possible to keep things afloat, but split that team in half and hire another manager and you'll be in a much better position.

What usually happens here is that your most senior members of the team are picking up management responsibilities instead of doing IC ones. By all means they should contribute to mentorship, direction, culture, etc. but there is way too much going on to have a deep understanding of those 15 engineers.

The only times I think this work is when the leader sucks, so swamping them with reports means they have a more difficult time micro-managing. But they're probably getting in the way in some other fashion.