There are lots of things here that we don't know... and people seem to be passing judgment based on incomplete information. In particular, we don't know the involvement of the parents. If the parents have been talking to each other, and have assisted in arranging the trip, and the families have checked each other out... then what's the big deal? We don't know this, and until we do we shouldn't judge.

I had several friends that I had never met when I was the OP's age - this was in the 1970s, long before the Internet, and they were my penfriends. And I took several international trips, as a minor, to go and visit these penfriends. The first such trip was the week before my 15th birthday - so I was considerably younger than the OP.

Most of my penfriends were female (like me), but there was a male penfriend to whom I felt romantically attached before we had met... and we did become boyfriend and girlfriend for a while, with both sets of parents supporting our relationship.

The Internet is making it a lot easier to make friends with, or become romantically attached to, people one hasn't met... but it's not a new thing at all!

If the OP is staying with the girlfriend's family, and the trip was arranged by the parents, then where is the problem?