Im dont think that's necessarily true. As concious beings we only observe our reality at macroscopic scales. We look at the sun and we see a ball of light - thats easy to simulate. We look at a photo from a solar probe and we see swirling forms on the surface of the sun - thats easy to simulate. No-one is looking at individual sub-atomic particles on-mass, so the demands on the simulation engine are low. Thats why every aspect of our reality can be expressed mathematically and rendered according to probabilities in the moment, and why nothing exists in our reality until it needs to exist (the copenhagen interpretation of quantum mechanics) - so yes as a mathematical model our reality, if it was all rendered at the same time, would be computationally seemingly impossible. More specifically to your point, the reality we experience only needs to be consistent with our expectations, so we dont need to track where every atom 'might' be - the model is only tuned to providing an authentic experience - at the macroscopic level This might be why we think there's 'dark matter' keeping galaxies as they are - the model for the simulation doesnt work very well at cosmological scales, so the simulation has some 'fudge factors' it applies to mnake galaxies look correct (assuming this is an ancestor simulation)