Eh, computational constraints are likely to be true in a large number of universes. There is no way to prove the universe isn't a simulation in a universe with arbitrarily powerful computers, but we can rule out universes with high constraints (like our own), or else test for things like approximations going on under the hood.
I think it's pretty unlikely, but it's possible and if a test confirmed it that would be incredibly important.
sure we can detect it from the inside, but its incredibly naive and arrogant imo to assume anything about the outside world. as a programmer i am very aware of exactly how much power i have over the insides of my target hardware - i can easily imagine creating a simulation where any 'life' inside of it would be subject to utterly different rules.
everything like conservation of energy, even the concepts of mass and energy, momentum, velocities, space and time are completely unrequired for the simulation. you would never ben able to guess these constraints from the inside without finding some bug or unintended behaviour - and even then, if you are used to a different set of concepts you wouldn't recognise the artefacts as being due to energy or mass constraints, the dimensionality of space-time or any of those things... there wouldn't be anywhere near enough evidence to draw that conclusion.
I think it's pretty unlikely, but it's possible and if a test confirmed it that would be incredibly important.