On big projects with large files (eg. cppquickfixes.cpp in the qt-creator project), the code completion is pretty slow. It needs 3-4 seconds to display something. I have disabled the "analyse current document" option, cpp-check and Clang-Code-Model -> Diagnostic config to no warnings, but also then the clangbackend process goes up to 100% cpu for 3-4 seconds. (If I don't change the file and call the code completion a second time it is ok fast (ca 600ms)).

I don't remember that I have these problems with QtCreator 4.13.x