You are seriously over working it. If you scan that much stuff that often and that long, you don't need a multifunction device, you need a dedicated scanner.
The 3315 runs 360Mhz CPU and 128MB of RAM, to put that into perspective, the original iPhone from Apple was released in 2007 (10 years ago) with a 412MHz CPU and 128MB RAM
To be fair, they are different architectures and very different products, I'm just trying to compare in layman's terms.
And it isn't that the printer can't do it, it just won't behave without a break here and there, so when the user goes to the bathroom, for a smoke, for a bagel, for a cry while wondering where they went wrong in life, have them reboot the thing to clear it's cache.