Thank you very much, oddworm! I was well aware of the problems you have listed, but after working on it for four months, considering my limited time, I've decided to find a more interesting project to work on. So, I couldn't optimize things further. By the way, your music sounds great! Perhaps I could borrow some for my next project, that is if I can make it. Again, this first project was more like a training for me. Hopefully the next one is going to be more fun! ^ ^
Oh, and I'm sorry for the escape button. You can simply change the order of levels in the "images" folder by renaming files, to start playing from further levels. :)