image optimizer for web

Hello,

This image is a poster I scanned in at 1200dpi in three sections, stitched in Photoshop 2021 and saved as a 12 quality JPEG. I tried the default settings, I tried lower settings and still no dice, neither with running as administrator. I'm on Windows 10, 64-bit.

I hope this isn't too niche of a use case, a program like this is ideal for working with large scans. Thanks for any help you can offer.