There is no good reason to think that we will in fact scale to the point where we can "simulate physics to the smallest quantum details, at a universal scale, at a fraction of the energy cost of our own universe". Computing cannot scale infinitely - we already have various limits based on our incomplete models of physics and there may be even more limits that emerge with further research. Even with a quantum computer, it's unlikely that we can really simulate chaotic systems with any real semblance of accuracy. Now, that doesn't mean that we can't approximate such behavior by implementing optimizations and abstractions on top of elementory particles but if our universe is indeed a simulation, it seems to not be employing any of these.

Indeed, the only two aspects of your universe that make the idea that it's a simulation even remotely possible is the fact that there at least appears to be an ultimate smallest division of physical attributes - the plank units and the fact that there is also a specific limit on the speed of causality - c. Neither of these are a slam dunk.