[Closed] Mousetool and lots of faces

Why does a mousetool becomes very slow in updating once you get lots of faces in your scene?
I update a box position according to my mouse point, it updates fast. As soon as I have an object in my scene with many faces (one object, or many objects with less faces), it drags the mouse update down a lot.

It looks as if mousetool is checking something on all available faces.

Any idea?

Thanks,
Davy