How to resolve '30 minutes remaining' issue during macOS 15.3.1 update on iMac Retina 5K, 2019?

I’ve had update issues before, and here we go again. My Mac shows an alert: Available updates: macOS 15.3.1 with the install buttons. But every time I try to install, it gets stuck at the exact same point, “30 minutes remaining…” The download itself only takes 20 minutes, so this makes no sense.

For reference, I have 500 Mbps download / 20 Mbps upload speeds more than enough to install quickly. Last time, I had to reinstall the entire OS to fix a similar issue. Am I really stuck doing this again? Should I just accept that as the norm now?

Honestly, I’m frustrated. Apple used to stand for seamless software and hardware integration. Lately, between my iPhone 15 Pro Max freezing, Apple apps becoming unresponsive, and now my Mac refusing to update, it feels like they’re making things so tedious that they’re pushing me toward new hardware or worse, out of the ecosystem entirely.

For context: I’ve been a loyal Apple user since high school my first computer was an Apple IIe, and I bought my first Mac for college, 2 years later (dual floppy drives, no hard drive!). That’s decades of loyalty, but this kind of experience is seriously testing it.

Anyone have a solution besides another full reinstall?

Thanks!

[Re-Titled by Moderator]