Qt Quick Designer Components does not compile with Qt 5.15

When trying to add component to qtquickdesigner-components repo with Qt 5.15.* it fails as Qt Quick requirements between Qt 6 and Qt5.15 differ. Qt6 does not require version numbers for the import and there is no branch for 5.15. There is branch for 5.12 but that is not up-to-date.

Solution proposal: Create branch for 5.15 that has same content as 'dev' with proper versioned imports.