Hi Maverick777,
Considering you have bad credit rating, 15% is not too bad. Obviously you didn't tell them it was a business loan or I doubt they would have quoted you at all.
You're quite right that your only other option is a secued loan, which can be right for a lot of people - you obviously don't feel it fits your finance needs currently.
If you are definitely going down the unsecured route, I'd take the 15% and hope your business makes cash quickly that will enable you to pay the loan off quickly.
Let me know how you get on.
Tim Moss