Very rarely do situations like this work out. I'd be very nervous on why the bank would fund most of it, but not all of it - clearly there is a risk there that they are seeing. Also, $15K is a hunk of money to donate on a really big maybe. Starting a business is rough, there are ups and downs, and as the "friends" you will be the last to be paid back, and that's IF you ever are.

You're not saying what the business is though, either. If it's an established business (say, a restaurant as an example) that has been doing well enough, and they are simply taking it over (and have the experience to do so), then I might be more open to the idea. Starting something from scratch, however, I would probably pass on investing in, at least until they can show how the bank's loan is getting paid back and money is coming in...