I just bought a new computer and used the same home system like before. Virtualbox was now really slow and it used also for small task 100% cpu. I searched through the web without finding a solution.
After a lot of testing i purged virtualbox and vagrant. Additionally i removed the directories .Virtualbox and .vagrant.d in my home folder.
Now i installed virtualbox and vagrant again and the performance was suddenly way better. I do not know what virtualbox stores for information but it really slowed down my system.