Adobe's Mukul Vinay Lele has written an article that includes a workaround for bloated project sizes that you might encounter in your Captivate projects.
According to Lele, "Adobe Captivate customers have always been very active on the forums. It has been a great place to interact with customers, resolve their issues and learn more from them. Recently our customer Paul Thrippleton raised a CPTX file size bloating issue in forums. Thanks Paul for raising the issue. We worked on it and have found out that the issue is seen because of the audio files (.wav and .mp3 files). Although we will be surely fixing it in the next release, the good news is we have an easy workaround to overcome the problem."
You can find the full article on the Adobe Captivate blog.