(macOS) Why is Lightroom very slow to reach full resolution (memory pressure upto 15gb)

Hey, @45pictures. Welcome to the Lightroom community. I'll help you figure this out.

What troubleshooting steps have you tried already? Does it slow down after a specific set of steps? Is there a noticeable pattern to this behavior? What version of Lightroom or Lightroom Classic are you working on?

To begin troubleshooting, test some variables like:

• Unplug any external peripherals & use wired input devices.
• Unplug external drives.
• Go to Lightroom > Preferences > Performance > Use Graphics Processor > Set it off if it is on Custom or Auto. If this shows you any differences, please check this article to troubleshoot further: https://helpx.adobe.com/lightroom-classic/kb/troubleshoot-gpu.html
• If you're working on Adobe Lightroom, please pause the sync while you're working & then resume at the end of your editing session to let it complete sync.
• If you're working on Lightroom Classic, reset preferences following the second (manual) method from this article: https://helpx.adobe.com/lightroom-classic/help/setting-preferences-lightroom.html

Let me know how it goes. Thanks!
Sameer K