Nope, as the other poster already chimed in.... wasn't me.
Look, there is a baby on the way...
The possible baby of the OP's 15 year old child.
The possible grandchild of the OP.
Nothing will change that!!!
Everyone, including me, has posted that at this point, what is done is done and the OP needs to proceed as positively as possible. (go back and re-read if you want...)
It is not that I am trying to be negative.
But, I have not heard ONE single word from the OP showing concern for her son... It is like she is almost happy (and proud) that her child is in this situation as it might provide her with an adorable baby. Not ONE word about what her son thinks. Not ONE word about how he is feeling, how her son may be being affected by all of this. Even possible criminal charges... 
I feel like I am seing some huge flags that others are missing here.
Within hours of getting the news, she is talking about moving the baby and the mother into her home.
And, as more recent posts have mentioned, this boy has been with this girl since he barely passed his 14th year of age.
NOPE, as the mother of an 11 year old son who will be that age before I know it... no way will my child be given that kind of opportunity and even encouragement at that age. This is my opinion... There are those who may disagree... But, this does not make me negative or snarky.
I truly am concerned for the OP's son.
Having said that....
Let's not sidetrack this thread bickering and pointing fingers at each other... For the OP's sake... Let's post to her regarding her current situation.