More aggressively cache computed images

I am doing a slideshow of 100 slides. Each of them have a full HD image on them and some of them have several.

Impress is re-computing the thumbnails of the pages over and over and it takes quite a while since it is only using one of my 8 cores.

I have tried the tip on Images slow down performace and that seems to marginally help. But the maximal cache size is 256 MB, and I might be hitting that limit.

Can I force LibreOffice to utilize more cores when generating thumbnails?

Can I force LibreOffice to cache more than 256 MB of images? Can I see how much of the cache I use?

Impress,, Linux

100 Slides with HD images is a lot! But what is the quality (number of pixels) you really need? Where do you want to show these slides. Cinema screen ~ 20mx 5m? I recommend to think about this.