Delete portion of jpg after clipping mask
I am making a poster (24 x 36) with multiple jpg photos (44 photos all different sizes) that I have sized using clipping masks. When I'm done and ready to export (both to pdf and jpg - either will work in the end), the file is too large to upload to the printing company. How can I either reduce the final size of the file (jpg or pdf)? I've tried flattening, but I don't think that's the issue.
I have read several posts on deleting excess content outside the mask, but they are all talking about vector items rather than photos. I'm wondering if there's a better way than the eraser tool.
I am using Adobe CC - Illustrator 24.2.1
Thank you!
Elizabeth