Some PDF files render very slowly

I build PDF files of cave maps which contains tens of thousands of vectors. The PDF files are created with Therion, which in turn runs TeX to create PDF files. In any Poppler-based PDF viewer these files take multiple minutes to render. On less power computers the same files will render in Adobe Reader in 3 to 5 seconds. Master PDF Editor also can render these files in a few seconds, though not as fast as Reader.

A sample file is attached.StarkCaverns.pdf

I use mostly Fedora 34. Poppler is version 21.01.0

Bill Gee