I was 18 when I got pregnant with my first daughter - I know that's not the same as 15, but it was still hard on my family. My mother was the most angry out of everyone. My dad, wanted to be angry, yet - part of him wanted to be excited too. It was the biggest relief when my dad finally said - from this point on we're going to be happy about this baby. I was about 5 months along at that time. Up to that point I was very stressed, worried, ect. all the time. My haven was my paternal grandparents' house. They were never angry, judgemental, etc. They never shouted, "You're getting an abortion!" the way my mother did. They never suggested that aborting my baby would be what God wanted like other family members did. I couldn't have done it without my paternal grandparents. This was where I went for refuge when the world around me was judging me. Wouldn't it be wonderful if your own home could be your daughter's haven during this difficult time?
I know it's hard and you're probably angry and confused, but this happens. This happens to good kids. It's going to be very difficult for everyone and I don't think that pressing charges on your grandchild's father will help anything. (I could see if he was like 25 or 30, but 15 and 18 is a pretty normal age gap for dating.) Every situation is different, and I don't know all of the details of yours, but I can tell you that your daughter is probably freaked out beyond belief and having you to support her will make her pregnancy less stressful. She may change her mind about adoption too. I didn't but I was older and done with high school at the time. I had a couple of friends give their babies up for adoption when I was still in high school and they both felt and still feel they made the right decision, but it took them until almost the end of their pregnancies to decide. Since then, I have become a teacher and had several students give up and several students keep babies. Either way it's a difficult choice, but it will be easier for her and ultimately easier for you if you and your daughter have each other.
You probably don't want to force your opinion on your daughter either - to avoid resentment, etc. However, I do think you and your husband should have some say in the adoption question. Here's why - there's no way she can do this alone - even if she's on welfare, she'll still need your help. I doubt you're ready to say - "Get your own apartment sweetie!" (At least, that's the feeling I get from your post.) So, since she is still a minor, her baby will be on your insurance, will eat your food, will require childcare, etc. You'll be footing most of the bill. I think you could wait to sort this out until you've had time to digest it, but you should start talking about it soon - nine months will fly by, so you will have to talk sooner than later. The ultimate decision will be the day the baby is born or shortly thereafter. I guess it really should be your daughter's final decision, but I do believe, as her mother and as her father, you and your husband should have some major influence over it. Major discussions will need to take place maybe in the presence of a counselor.
And this is important- Don't blame yourself mom! Kids will do what they want to do and if you try to stop them, they are crafty and will figure out ways to do it anyway. I know I did. And I was overall a stereotypically "good kid" - weird, but good.
Bottom line - be there for your daughter - even if you are angry right now. Try to help your husband work through his anger too. Many times situations like this require counseling. Chances are when you and your husband meet your grandchild for the first time, the troubles will melt away and you will figure out a way to make it work. As angry as my parents were - in the end, they were my biggest supporters. And, in the end - my daughter changed my life forever. I shudder to think of where I would be without her. As cliched as it might sound - everything happens for a reason!
My daughter is 11 now and she's wonderful. My family can't imagine life without her. My husband is not her biological father, but he is her dad and always will be. And, lo and behold, when she was 7 her biological dad came back into her life. They've had a good relationship for the past 4 years. Like many of the dramas of life - it will work itself out. It will be hard, but by the grace of God, you, your daughter, your husband and that baby will be all right. God bless. My prayers are with you.