Check the tab. If 5.15.2 isn't listed, click "Add" and browse to the qmake.exe file inside your installation's bin folder.
This is where the frustration lies. Here is a review of your options to get 5.15.2 without a commercial account: qt 5152 offline installer
Here’s a solid, step‑by‑step guide for — a popular long‑term supported (LTS) version often used in commercial and embedded projects. Check the tab
Why Qt 5.15.2 requires manual download (and no online installer) qt 5152 offline installer
Due to Qt’s change in open-source policy (post-2021), the offline installer is no longer linked from the main qt.io/download page.
(LGPL/GPL v3).