lazytest | A continuous test runner for Go | Continous Integration library

I have some code that generates large amounts of instances of a small data class. When I added one lazy property to the class I noticed that creating instances of this class became much slower even if the lazy property is never accessed. How come this happens? I was expecting that there would be no difference if the lazy property is never accessed. Is there any way of using lazy properties without taking this kind of performance hit?

Here's a minimal example:

I want to implement custom Lazy class, just to implement it. What is interesting is that when I pass function to constructor, in debugger I can already see that the object has been created inside the function even though the actual call is inside Value. Is this because debugger evaluates the _func itself or do I just don't understand how Func<> works?