Qt 5.15.3 version bump with binary path changes
Up until Qt 5.15.2 we were using qtchooser to provide unversioned links to Qt binaries in PATH, like qmake, moc, qmljs etc. Starting with 5.15.3  such links will be installed by each respective Qt package and '5'-version-suffixed, e.g. qmake becomes qmake5, qml becomes qml5 etc., mirroring Qt6.
If you develop with Qt5 and rely on unversioned binaries for your workflow, dev-qt/qtchooser as a tool for quickly switching between multiple Qt installations (e.g. Qt3, Qt4 and Qt5) can still be manually installed. The 'default' Qt version in PATH is then controlled via config in /etc/xdg/qtchooser.
Otherwise, dev-qt/qtchooser will be slated for cleanup on your next emerge --depclean run.