Hi. I am the developer of the plugin.
Loading is slow because of the massive terrain, mostly. So if you load only the buildings it will be much faster. To do that, try running the loader from the processing toolbox:
Then you will have the option to filter objects by area (bounding box) or type. You’ll also have a nice progress bar to track the progress!
You might want to read this as well.
PS: Sorry for responding in English, my Dutch is not good enough.