I'm still a newb, but even I know you are going too fast. It's been said a million times, nothing good comes fast in this hobby. Slow down. Take your time. Wait for the tank to cycle and use the time to read posts and educate yourself.
What does a 15 gallon hang on mean? Is the water volume in the filter 15 gallons, or is it rated for a 15 gallon tank? If you have a total of 18 gallons, you still stand a chance.
Andylee is just trying ro help out like everyone that wrote you, just absorb the info and do a little bit of research and you'll be set, when your ready for the zoas I have there yours.