Compressing one image is easy. Compressing 50 is a different problem. Here are the fastest ways, ranked by how much time they'll save you.
XnConvert handles bulk image compression with a visual workflow. Add a folder of images, set output format to JPG at 85% quality, and run. It'll process hundreds of files unattended while you do something else. Free for personal and commercial use.
mogrify -quality 85 -format jpg *.png — one line, converts every PNG in the folder to compressed JPG. Install with brew install imagemagick (Mac) or apt install imagemagick (Linux).