Can the graphics cache size be increased?

I’m aware of the graphics cache option mentioned here, available in Impress through Tools → Options → LibreOffice → Memory. Unfortunately it seems the largest allowable setting is 256MB.

I have 16GB of RAM and a long presentation packed with high-res images and video. I’ve noticed very significant slowdowns, especially when copying slides between different presentations. Closing and re-opening the presentation seems to fix the problem. I don’t know for sure that cache size is the cause, but it seems like a reasonable explanation and I’d like to test it. Is there any way to let LibreOffice use more cache?

The value cannot be increased (that I know of). There are known image caching / management issues in LO. Refer my answer here. This thread is also related.