I don't think you're right, at least on my computer. I've got two 99.5 GB files listed on my computer - one called iPhoto Library.migratedphotolibrary and one called Photos Library.photoslibrary.
Hard links can be confusing, because they cannot be distinguished from the original files in the Finder.
The links between the original files in the iPhoto Library and the Photos library are hard links. A hard link to a file and the original file are both referencing the same entry (inode) in the file table. This way each of them is a regular file, but they are sharing the blocks on the disk. Because both are regular files, the Finder will show the full file size for both of them, and both your photo libraries will show the full size.
When you delete the iPhoto Library migrated, you will reclaim the disk space used for Previews , Thumbnails, and Faces, but not the disk space used for the Master folder. They will only be released, when you deleted the photos from your Photos library as well, since the files are shared.
See this link: Six Colors: The (hard) link between Photos and iPhoto
And Apple's document: Photos saves disk space by sharing images with your iPhoto or Aperture libraries - Apple Support
The original files in Photos are hard links to the original files in Aperture or iPhoto, but look perfectly identical:
The same original master file in the migrated Photos Library as in the original iPhoto Library:
You can tell that it is a hard link from the identical inode number in the Terminal using the "ls -i" command:
I marked the inode numbers in red: The files are in different Masters folders, but have the same entry in the file table:
Last login: Sat May 23 07:46:46 on ttys000
Hermione:~ dreschle$ ls -i ~/Pictures/Aperture\ Library2015.migratedaplibrary/Masters/2015/05/23/20150523-185458/IMG_0107.jpg
37677881 ~/Pictures/Aperture Library2015.migratedaplibrary/Masters/2015/05/23/20150523-185458/IMG_0107.jpg
Hermione:~ dreschle$ ls -i ~/Pictures/Photos\ Library2015.photoslibrary/Masters/2015/05/23/20150523-185458/IMG_0107.jpg
37677881 ~/Pictures/Photos Library2015.photoslibrary/Masters/2015/05/23/20150523-185458/IMG_0107.jpg