QGraphicsView performance recession

Reproducer attached. A QElaspedTimer is used to measure the time spent on QGraphicsView::paintEvent (main_window.cc line 57). And result is printed out. The paintEvent() is going to be called every 1000ms so the result is quite stable and statistically-valid.

The original reporter claims the following numbers, comparing Qt 5.1 to 5.15. The reported numbers are:

QT5.1.1 : 33 ms
QT5.15.10 : 81 ms

I cannot confirm it is true or not. I don't have the same environment, nor Qt 5.1. And Qt 5.1 is not supported whatsoever. But I've tested 5.15.16 vs 6.5.5. And this is what I can conform;

QT5.15.16 : 12 ms
QT6.5.5 : 18 ms

Note that I am not saying Qt5.15.16 gets a huge performance boost. I am very likely testing on a much better HW than original reporter did. But the number of 5.15.16 and 6.5.5 may still mean something.