GIMP Version: 2.10.12
Operating System: Windows
OS Version: Windows 10
GIMP Experience: New User

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I'm sketching a very large map (with a tablet), and having trouble when changing layers.
I appear to be CPU-bound on (only) two cores.
It takes 20 seconds at least when selecting new layers. Windows will say 'this program is not responding' sometimes. Waiting fixes the problem, but it's sometimes quite a wait. These layers are small - just place-names for the most part. Moving the layers and changing visibility/movability/editability can also take a while.

The actual process of sketching is actually fine.

Image size is 27872 by 19652 pixels - which I imagine is the big issue somehow.
600 ppi
Colour space is RGB.
File size is 600MB, and 2.3GB in memory.

My hardware is quite good. I'm in no danger of running out of ram, I have 32GB, and Windows task manager has me using about half of it. My GPU is barely doing anything. There's no reason for my computer to be going back to my storage drive, but even if it was the image file is on a fast drive.

Software-wise, I've set Gimp's Tile Cache size to 28 GB; it was previously 16GB and I've noticed no difference from the change. I upped the other cache sizes as well. No difference.

What I have noticed, is that looking at Task manage when the Gimp pauses (when moving my small labels around), my computer uses two CPU cores fairly intensely. Since these are small labels, and I have significantly more cores than two - it's disappointing. A lot of bother (and work) is being created inefficiently to make a rudimentary change.

Anyone have words of wisdom? I'm reluctant to cut up my map unless someone has particularly clever tricks to keep the map pieces relating to each other.