You have a very curious definition of universe, not to mention you are reasoning by analogy.

Computer simulations are the interactions between transistors in a CPU, carried by electrons and photons. Dreams are impulses in the neurons of our brains that happen to get stored as memories when we awaken. Our imaginations are also physical processes that take place within our brains. All three of these are on a vastly smaller scale than the universe we inhabit.

Do you have some evidence that the actual universe is any of these things?

A computer simulation isn't coherent in any way without a program. That most certainly points to a creator. Same as with playdough or clay: no animal or farm is gonna make itself.

But what evidence is there that our universe, the one we live in that appears to be roughly 14 billion years old, is anything like a program or a clay farm?

what evidence is there that it isn't? I don't know of any.

That's not really how evidence works.

You are describing the processes in our universe that allow the existence of the created universe. From within that universe, the actors would have no knowledge of these processes or even the existence of our universe unless the creators explicitly provided them with this information. To them, their universe would appear to be everything in existence just as ours does to us. That is why, to me, these universes are analogous to our own and since they are the only universes we know to exist besides our own (even though they exist within our universe), I think it makes sense to consider the possibility that our universe is no different and that our universe may exist within a parent universe and that our universe has a creator in the parent universe just as our child universes have creators in ours.

As far as evidence goes, there is no tangible evidence (and if the theory is correct, it would probably be impossible to get evidence unless the creator allowed it) but if you have 100 bags and in 99 of those bags there is an egg, it can be reasonable to assume that there is an egg in the 100th bag. That isn't really evidence though especially because that 100th bag is different from the other 99 as it contains them. It could be argued however, that this is is a type of evidence. I'm not sure how exactly but I think someone smarter than me could.

Regarding scale, I don't think that that is such an issue for three reasons:

1) If something is contained in something else, it is reasonable that it's container is larger so just as our universe is on a larger scale than our child universes, our parent universe could be on a larger scale to our own.

2) Only the actors and what they observe need to be simulated (I may be the only actor, maybe it's you) the rest can be approximated. Perhaps this is why it is so difficult for scientists to come up with a unified theory. Maybe macro and micro events within our universe are simulated in different ways and the simulator that runs our universe is inconstant when these two simulations need to be merged.

3) Perhaps it takes the equivalent of years in our parent universe to simulate a second in our universe maybe this very moment is the only one that has been simulated and the past is just the initial state.

edit: The bag/egg analogy isn't great but I am sure that you know what I mean.

Almost everything complex we see in the universe has a simple explanation. The galaxies/stars/planets formed because of gravity. Evolution is small gradual steps. Most science equations could fit on 1" of paper. Why would the universe's origins be infinitely complex rather than simple? Why is everything we've ever discovered natural, but the origins are super-natural?

I don't quite understand your reasoning. A creator as an explanation for the origins of the universe is as simple as anything else.

Where do the rules of physics come from? (i.e., where does nature come from)