If there are many files open, holding down Ctrl+W is very slow way to close them. I suspect this is because Qt Creator probably doesn't hold all of them in memory and it loads a file again once an old file becomes visible again.

Maybe best way to reproduce is to open many files, then restarting Qt Creator, restoring the previous session and holding down Ctrl+W.

There is Ctrl+Shift+W which is much faster if one wants to close everything, but often one wants to only close many, but not all files.

Perhaps this (if it is re-loading the file) could be made asynchronous so the closing feels better.