UpdateI've researched the problem a bit more and the "Web Protection" in Avast Antivirus is what causes the problem since NHS is creating too many threads that take forever to get killed and time out (being able to set timeout please?). Therefor one get a huge stack of idle threads that lag everything. Disabling Avasts Web Shield somewhat solves the problem.
So to all you that have problems, check your AV and configure it if you can or request timeOut-features in NHS.