I have found several things to be helpful when trying reducing the size of the course (which might help with page load times).

Just before publishing a course I click Module>Delete Unused Files.

I've also found Audacity (free sound editing tool) to be a big help in manipulating sound files to make them smaller. I use .mp3 format audio files.

I do all my image editing outside of CourseLab. I use .png file format most of the time and make sure the images are exactly the size and shape I need before bringing them into Courselab.