Keep a local copy for long-term project maintenance.
Why specifically hunt for an offline installer when the official Qt website pushes the online installer? qt 5152 offline installer
You can still access Qt 5.15.2 via the online installer's archive feature: Overview of Qt Installer Framework - Qt Documentation Keep a local copy for long-term project maintenance
(Note: I can suggest related search terms to help you find downloads.) qt 5152 offline installer