For the question that the compressed folders on your device are not very compressed, it's because you haven't set the compression rate to lower quality. You can simply determine the image size by reducing resolution here: go to Applications and launch the Preview app > click on File ➙ Open > navigate to the photo you want to compress and select Open > click Tools on the menu bar > choose Adjust Size > choose Percent or Size as adjustment value.
You can either upgrade your macOS 10.10 to 10.13, then you can use the help of a third-party toolkit, iBoysoft MagicMenu, which saves you time and effort by compressing your images to smaller sizes easily.
Step 1: Free download and install iBoysoft MagicMenu on your Mac computer.
Step 2: Right-click on the selected folder or files and choose Compress.
Step 3: Set a password to protect files and folders on your Mac. (Optional)
Step 4: Choose a compression level from the High level, Middle level (default), and Low level.
Step 5: Click Compress and select a destination to save your compressed files.