alice, the weird “textures” you are seeing are actually vertex colous - the texture is lost with the simplification because the geometry changes and therefore the unwrap is useless.
How is the time difference of texturing a full resolution mesh as opposed to a simplified one? I always thought a simplified one takes shorter, but I have heard people claim the opposite. How is this in your experience?
When 3D view is active (blue frame) then you can set quite a few settings on the Scene tab (blue).
Is it possible that in your textured model Sweet is not available?
That would be a possible solution for your main issue, in as that you don’t actually see the texture due to memory limitations but only the vertex colours…
The reprojected textures on the 100k model look alright.
Due to the geometry that I’m dealing with, I think even 1k tris is already very high since the blurred texture occurs on an almost flat surface, right?
From the view there I can confidently tell you that the 1k model is definitely far too much simplified. If you look at the top left corner of the masonry bit, you can see that the model is slightly chamfered where in reality it is more or less 90°. Also, the recess of the plaster is not at all shaped as it should be. The reason for the blurriness is that RC is trying to project the texture from the images onto a surface that does not exist like that in reality. From different angles you get different colours, hence the blurriness. If you definitely need such a low poly count, then you need to use external tools to recreate the geometry as closely to the original as possible.