Your parents won't co-sign?
You do what you gotta do. Like the old adage, you got to spend money to make money. 4.5 times does sound awful high. What's the intrest rate on this? My last loan was through Sallie Mae and I think the rate was 4%. Is this $15,000 for one year or several? Did you shop around for loans and compare?
Last year I enrolled in a very expensive private school. Many people had very negative things to say about how much I was paying (such as ridiculous to pay that much, that's stupid, etc), which was ~$21,000 a year. BUT I got so many grants and scholarships
that I never even applied for that it lowered my tuition to less than $5000. That's cheaper than tuition at most public schools.
Are you planning on working any during school or on breaks? If so, hoard that money! Also, if you're not already, consider becoming an aide. Where I work, and most places have this, if you are studying nursing they will pay for a portion of your tuition with an agreement that you work for them so many months or years after - depending on how much they paid.
If this is what you truly want, then go for it! Look at grants and scholarships. There's a scholarship
out there for everyone. Talk to financial aide and get ideas. Good luck!