You're talking about is blend of Ghost in the Shell and Holographic Universe Theory.
The only thing being rendered is what's necessary to make you think you're somewhere, while saving processing on not rendering anything outside your field of vision.
But then you're also stopping short.
God wouldn't be the computer.
God would be the Architect of said Computer, the Programmer, The OP, The Beta Tester, Player 1, The Debugger, the Updater, etc etc.
If you'll expand your thinking (if you remember that from Q), you'll understand that "God" wouldn't even need to be actively paying attention to The TechKnowLogos Computer.
All that would be needed is a dongle connected to the higher reality's WiPhi, pulling in NEW*UNIQUE additions to our lower perception of Existence, and also would AutoDebug, AutoUpdate, and AutoCorrect.
When does that happen? When you run through the simulation, AGAIN, without getting the point.
It's also what makes "God" God.
Even if (You) knew everything about everything as it is and did all the things forever throughout time, you would not be able to add anything new that isn't already in Existence.
That +1, that Absolute Continuance…
That's at least one major distinction.
It's also why you never need to worry about accidentally uttering the Name of God and gaining control of Them (think summoning demons, same principle) because even if you were to somehow produce the vibrations that are recognized as ALL POSSIBLE AND IMPOSSIBLE THINGS, you wouldn't have time to do anything about it because that name is updated every passing, infinitely small moment.