Project file size too large

Hi again, I just have a question that I hope someone can shed light on. I created a project with an audio file (mp3). My concern is that the project file is very large (200+mb) even if the mp3 file is only around 10-15mb in size. The project only has a few slides containing a few texts and a single picture. Though the published file is only around 7mb, my concern is the project file size. I already checked library tab and clicked on unused files and it didn't find any. Is this normal?