Issue didn't turn out to be RAM at all, but path names that were too long, silently failing when it tried to move assets during the build, which led to a lot of trash remaining in the RAPT asset directory (which led to the buid jvm exploding in memory etc.).
Now the cause is fixed, the builds are quite well behaved and fast again, and the RAM upgrade wasn't needed after all (other than that it helped me actually complete a build, find a curiously bloated APK as the result, and from there work my way back to the cause).
As to previous suggestions for handing it to the community to fix, well in this case a) they would have run into the same issue and b) a dev needs to be able to support his own product.
What you want for rendering is VRAM and cuda cores, e.g. the memory and processors on your graphics card. With two NVLinked 2070Supers I got that covered, at least for my needs. CPU and RAM aren't really all that important.