Epic failed with QFileSystemModel performance

Resizing and/or browsing a file system is ridiculously slow:

QApplication l_qApp(in_argc, in_argv);

QMainWindow l_window;

QFileSystemModel l_sys;

l_sys.setRootPath("");

QTreeView l_view;

l_view.setModel(&l_sys);

l_window.setCentralWidget(&l_view);

l_window.show();

l_qApp.exec();