One possible solution is to elongate the time-steps; if we take a million years to simulate one second of simulation time you could get by with a lot less computing power.
If you do that, and load some information from a slow storage device (hard disk), calculate on it for a hundred years, then write it back, load some more, repeat, until you have computed "one planck time" accross your entire simulated universe...
... at what point in the loading, crunching, saving, does the information inside feel concious and self aware 'in realtime'?
Since this could apply to your life being run on a different substrate, with no actual effect on your perception, I don't see how this is a useful question.
The problem is that the scales involved are so ridiculously large that it could easily take 1 billion years to simulate one second. Even with 1 million years per second, simulation of a thousand years would require something like the age of the universe to compute. In that case, these "beings" could not be our descendants since they live in a universe with different laws.
Actually, at a million years per second, the age of the universe (so far) would go by in five simulated hours. I don't want to speculate on how long we have until heat death, but I doubt it's long enough to simulate a single human lifespan at a million years per second.
