Do you find a guest toilet next to a living room wall disturbing? Can you always hear the flushing there?
You can hardly hear the toilet next door, only the cistern is adjacent. You would hear a toilet one floor above - in that case, it would be the soil pipe whose acoustics you would "enjoy."
Was the wall deliberately built so thick?
Load-bearing walls with a thickness of 24 cm are not really exotic; in the past, the nowadays more modern thickness of 17.5 cm was used less often. But in any case, you don’t hear the wall thickness, but rather the slurry with accelerating fall.