User Interface very slow and freezes after a project is opended

After the upgrade from Qt Creator 4.5.0 the user interface reacts very slow if a medium to large project is opened. Even if it looks the project is completely loaded the user interface seems to not very responsive compared to Qt Creator 4.5. Even opening a couple iof source files in a row  makes the UI very slow and shows a cpu load of 15%-20% for about 10-15 Seconds. Such a behavior i did not notice with Qt Creator 4.5. So the Creator is not usable for me.