Each state is different in how it could be handled and within a state, such an issue may depend on which judge you would get. However, for a 15 year old, I think it would be less of an issue than if the child were younger (and considered more impressionable). If you have a good relationship with your ex (he won't try to dick you over) then you will probably be ok.
I think when you tell someone, let the excitement come through and I think people will not react too negatively. They may be concerned and try to give some advise. But you can counter with stuff like "living life to the fullest" or "taking the path less traveled" or "we are all happy, so what's the problem".
Let us know how it goes when you tell someone. I am curious to see what reactions you get.