If you really can't keep anything down, even sipping something, you really should call your provider and get iv fluids.
I dint know how it can affect baby just from dehydration alone at 15 weeks, but you're also looking at increased risk of uti which can be harmful if you dint get it taken care of.
I was in l&d Friday night from Braxton hicks every 5-10 minutes. I thought I was drinking plenty, but it turns out I was very dehydrated (which was diagnosed after a full 1,000 ml iv bag, so was likely wise off before - and this www with me thinking I was drinking enough). I passed out shortly after arriving. I'm not sure how much of that had to do with dehydration, but I do know that I had almost passed out before when I was very likely dehydrated.
I would call if you can't keep anything down.