Nobody can tell you how difficult this piece is. It's all based on your own strengths and weaknesses.
You need to spend time with it yourself to figure it out.
Before you ask for help - in any life situation! - you should be prepared to answer "What have you tried so far?" Otherwise you look like someone who wants things handed to them, and that's -really- not going to work for a learned skill like piano.
Do what j_menz said.
Although I have some questions.
What are you auditioning for?
When are you auditioning?
What are their listed audition requirements?
Why do you think they want to listen to a entire 15 minute concert piece?
What does your teacher think?
What has been your most difficult piece so far?
How long did it take you to learn it?
Are there any recordings of it?
The listed requirment for repetoire is a prelude and fugue from Backs wtc
Three etudes but only one etude per composer by Chopin,Liszt,Bartok,Debussy,And Ligeti
The first and last movement of a sonata
And a large scale work(10-20 minutes) by a romantic or modern composer
The most difficult piece I can play is chopin op.10 etudes though no.12 and 7 are sloppy it took me two years
My teach says I can pull this piece of but I'm not sure about her word because she extremely optimistic