JPEG is 20th century technology. There are much better image compressors that are widely supported. Not well known, WebP is supported by all the main browsers and yields quality comparable to JPEG at half the size. WebP was royalty free answer to HEIF (which has not been well adopted due to Apple owning the rights). AVIF is generally 30% smaller than WebP and 50% smaller than JPEG. With the right conversion tool (I recommend Image Tool+), then are more options (like chrominance subsampling selection) to tailor the compression to your needs.
But SP doesn’t support AVIF. Please like my feature request here https://community.synology.com/enu/forum/1/post/196211