TMS Support >very< quickly came back with a result: lots of cells in the grid are filled from files where for double byte character content the appropriate font is not installed locally (the app is a log scanner, the grid shows summary of issues found from any installation around the world, these produce local output).
With fonts missing, PDF export gets into some looping to get the display correctly it seems. This is eating up the memory, in case of my 32bit example above the 2GB limit, 64bit version can handle the increased RAM requirement.
For comparison: I created a test bed with all locales working locally, took 4 times the number of files and producing a PDF that as a result is also num pages times four. In this clean setup the PDF creation consumes under 20MB...
TMS Software: thanks for your help!