The version you're trying to add does not exist at that URL:

$ spack checksum py-pyqt5 5.15.2
==> Found 1 version of py-pyqt5:
  
  5.15.2  https://www.riverbankcomputing.com/static/Downloads/PyQt5/5.15.2/PyQt5_gpl-5.15.2.tar.gz

==> Something failed on https://www.riverbankcomputing.com/static/Downloads/PyQt5/5.15.2/PyQt5_gpl-5.15.2.tar.gz, skipping.  (All fetchers failed)
==> Error: Could not fetch any versions for py-pyqt5

The version you're trying to add does not exist at that URL:

$ spack checksum py-pyqt5 5.15.2
==> Found 1 version of py-pyqt5:
  
  5.15.2  https://www.riverbankcomputing.com/static/Downloads/PyQt5/5.15.2/PyQt5_gpl-5.15.2.tar.gz

==> Something failed on https://www.riverbankcomputing.com/static/Downloads/PyQt5/5.15.2/PyQt5_gpl-5.15.2.tar.gz, skipping.  (All fetchers failed)
==> Error: Could not fetch any versions for py-pyqt5

I had the same problem. There is documentation on the site for the version but, from https://www.riverbankcomputing.com/software/pyqt/download, it looks like a 5.15.3 dev version is accessible.

@Sinan81 was going to take a look at updating the PyQt packages to use the PythonPackage build system. It may be possible to download them from PyPI instead which would be more reliable.

Closing as stale, but feel free to reopen if you want to continue the discussion.

sorry for the late reply. old pyqt packages can be obtained from internet archive's wayback machine. If Spack has a source tar file cache available on the internet, it would be nice to put these older tar files there.

#32696 also updates this package with the latest version.