Immutable vs mutable performance

I've stated before that I believe immutability should be used by default, and mutability is actually an optimisation technique.
Opponents of immutable data structures usually states immutable data structures are very inefficient. Of course I decided to test it myself.
The code is available here and you can try it yourself. I will only present final thought.
Immutability costs us performance. For big data structures as well as for bigger ones. For a structure that was about 20kB big, the test consisting of creation of 10000 objects took almost 20x time more for immutable value-object than mutable.
So now I have some questions: how often do you create 10000 objects? Is this a cost that we can take? If we use it for highly optimized algorithms - absolutely not. But for logic that should be primarly very well tested and stable, and free from surprises - yes!