I can't comment for pyQt. But the regular C++ Qt app I'm tinkering with at the moment uses 11MB private and about 50MB in shared memory for displaying a simple window with some nested widgets and scrollable lists.
for reference, the app I'm working on (https://ossia.io), a
multiple-hundred-LOC Qt-based DAW with support for many network protocols and which uses most Qt libraries as well as boost uses itself 41 megabytes of RAM (private working set) and 70 megabytes total (working set) with a small document loaded, according to the windows task manager.
