We're not picking on you, hon, we just don't want you going out there in public and saying 'and now I'm going to play this song, it's a little diddy called the Polonaise in such and such a key. We're trying to spare you the embarrassment.
OK, now, the reason this sounds fishy is that you talk about playing in front of 15,000 people, or whatever, but I think we all would like to know why? Who invited you? How old are you? What is the event? Not many people play in front of crowds like that - and then ask questions like 'Is this hard piece, right out of your level 7 book. Usually, to get to a level like that, one would know the repertoire better than you seem to, and certainly, be preparing for this for perhaps a year, not 2 months. Have you played much in public before? You need to be way over prepared for something like this. Good luck.
piz