A good number to try for jvm.ini is 1024. That's already 8 times the default for CS6, so should help quite a bit. Setting it to something too high could cause the system to run out of memory.
One thing to think about doing is to take say the first 6000 frames and copy those into a new FLA. If that succeeds you copy the remaining frames into a second new FLA. Then close the original FLA it without saving. So, you would have:
part1.fla //the first 6000 frames of whateveryoucalledit.fla
part2.fla //the remaining thousands of frames of whateveryoucalledit.fla
You can always go back to the troublesome huge FLA to get anything that didn't copy across ok, but you would then start to work on the two new FLAs.
A lot of things have been improved since CS6, especially with auto recovery. But some of the CS6 features were dropped in later versions, or work in a different way. But it's worth thinking about getting a more recent version to work with.
Once you have finished the animation you could copy the part2.fla frames and paste them at the end of a duplicate of part1.fla, and hopefully be able to save out a fresh complete FLA.
When I switched it to 1024xmx I still get the Java Runtime error, and I can't copy and paste multiple frames now into a new file or even the one I am working on, flash cs6 won't allow me anymore, I wanted the recent version of flash but the only one I get offered in my app preferences in creative cloud is flash cs6, I am guessing my computer can't handle it or something but I don't know how to get newer versions. Thanks for your help though Colin.
If you have somewhere to post the FLA online, where I can get it, I could try the copying idea for you.
I have sent you a message with a link. Thank you
I saw a message from you earlier, but it was empty. You can send a link straight to me at colinholgate at gmail dot com.
For anyone following along (though it looks like nobody is), Tristan has drawn his animation just as timeline vectors. Each time there is a key frame in each layer, that's like having a completely different drawing again. There are a lot of keyframes in the animation, and so although the file is only about 240 MB (72 MB of which is the sound), there are perhaps millions of vectors being loaded into memory. Hence needing 14GB of virtual memory to open it.
I've given him some advice, mainly that using symbols is a good thing.
For what it's worth most professional animation houses use Flash or Animate to animate individual scenes and not an entire film in it. To make an entire film in Flash in one shot would indeed bog it down and cause the errors your seeing. I recently made a 5 minute animated piece but even that was bogging a bit here and there. I know this doesn't necessarily help after the fact but you should make each scene it's own file and then export them to video files and edit in your video editor of choice.