Re: iPhoto or Aperture Libraries

Yes - once you have migrated to Photos (you never import a library) there is no connection between the libraries and you can delete the old one but it is not recommended nor is it needed - you may want or need the old library and deleting it saves very little - Photos saves disk space by sharing images with your iPhoto or Aperture libraries - Apple Support

Generally it is best to keep it for three or more months just in case and then to archive it before deleting

LN

Can I delete my iPhoto or Aperture library after I import my photos into Photos for OS X?

There are two reasons you may want to keep the original library:

1. Not all content can be migrated exactly as it has been in the original library, see this document: How Photos handles content and metadata from iPhoto and Aperture - Apple Support
   You may need to compare your books, the metadata, or even the edits to the versions in the original library to be able to reconstruct them.And it is not bad to be able to open the libraries in Aperture or iPhoto side-by-side with the new Photos library to compare them. One big problem with the migrated Aperture library was that many of the Aperture adjustments did not migrate correctly. The migrated photos looked spotty, and I had to revert them to the original and start over. Most of the smart albums were either missing or did not work, because the constraints I used are not available in Photos.
2. If you original iPhoto Library or Aperture Library had a slight corruption, the new Photos Library may be corrupted as well, and you may need to repair the problem in Aperture or iPhoto and then migrate the library again. Or you may want to merge libraries, or restore a previous version from your backup, or reconnect missing originals. All that may require to fall back on Aperture.