Complicated geometry lower in a model makes slicing simple upper geometry take forever

[slavedas]

What happened?

I'm working with some Lithophanes that I'm laying down on the bed on purpose. I'm finding that the complicated geometry slices fairly quickly (within a couple of minutes) but the border of the lithophane can take hours to generate perimeters - even when those perimeters are in fact only rectangles sitting on top of other rectangles.

I'm using the classic slicer and solid monotonic infill.

Project file & How to reproduce

blueprint_of_a_tower.zip

Version

2.5.59.0

Operating system

Windows 10

Printer model

Ender3/Switchwire 0.4mm V6 Stealthburner CW1