So when saving, the game probably does 'pause game->write game state to disk->resume game'.
So, when we are saving, it just goes through every object currently in the game, and writes its stats to the save file directly.
In this approach, the write speed to the disk is the bottleneck, since computation time is negligible on such operations.
But what if we wrote the game stats to RAM (no, the footprint won't double, its just 15 MB of text).
Now, we resume the game. But we are not stopping saving here, we are starting a new low-priority thread that takes the text from the RAM and saves it to the disk.
(The outcome will be the same, and you will only loose your data if the PC is powered off while saving, which would happen with the direct approach, too)
Yes, we still need to pause the game, but gathering 15 MB of information and writing it to RAM is a matter of milliseconds. You still need to write that to a disk, but that can happen while the game continues.
There are good arguments for 'pausing the game' while writing the save file.
Firstly, it takes time to write all the objects to disk and you don't want objects moving about in the interim. Also it allows more resources to be thrown at the save operation, meaning it is finished sooner.
That is exactly what I wrote about in the original post.