Wow, that is so sad. We had a 15 year old foreign exchange student a few years ago. At the time I considered it a bad experience, but this answer is going to be very complicated. First, we decided to participate in the program on the spur of the moment because we were told there were 60 kids who needed homes for the year. My heart went out to them, so we took in this student even though we really didn't have room. My boys were 4 and 10 at the time, and we moved them into the same bedroom for the year. We put our exchange student in our 4 year old's room.
The problems we had were that our house really isn't large enough for 5 people. He was with us for 11 months, and it was cramped. Also, he was 15, and he wasn't raised in our family. He wasn't used to having to put away his things (we're neat freaks). He was also HUGE, and he didn't consider there were 4 other people that needed space to sit also. He was 6 feet tall at 15 years old, and he would stretch out across the couch leaving no room for anyone else. Little things like that built up and caused major resentment over time because he never changed his behavior. He also picked on my 4 year old constantly. My boys get along well, so this drove me nuts. I mean, he's 15. Leave the 4 year old alone if you can't be nice! It was his way of playing, but my son hated it.
Cost was a major issue too. I had no idea how much it cost to feed a growing boy. This was a good lesson to learn since I have two boys of my own, but we weren't prepared for the cost of feeding a foreign exchange student. Also, if we were going to have him in our home, we were going to treat him like family. That meant gifts for him every time we got gifts for our boys. That added up to a ton of money. We also paid for movie tickets, dinner out, etc. It was extremely expensive.
He was a very happy boy, though, and we learned a ton about each other's cultures. He ended up calling me "Mom," and we all ended up loving each other. He tells me he loves me and misses me every time we talk. It was very challenging, and I don't want to do it again unless we move into a larger home, but now I treasure my relationship with my "German son." We are very close still. We email and skype, and my boys still talk about him all the time. He asks my husband and I for advice (he's in college now, and just started his first real job). I often email his mom, too.
So, although it was challenging, it was rewarding, too. I love him, and we're making plans to see him next summer. I hope things work out for your friend, and I agree with you. Your friend should try to work it out. It's a huge step to travel to a foreign country, and maybe 15 is too young, but now that he's here, perhaps your friend could work with him a bit longer to help him with school and adjusting.
I'm sorry this got so long. I hope it helps.