That's kinda what we do, my mom placed my brother's IS300 and her RX300 on her name however couldn't place my car because I think there is a limitation to it. My dad doesn't work in this country so he couldn't place it under his name, therefore, my car is on my name and since i'm 19 it's quite costly.
However, i'm getting closer to 21 where the insurance rates go down so thats good in a way...
Compared to your $15,000, my insurance is looking cheap now lol...then again your family has 5 cars, we have 3