and again exactly the same answer

You do not have duplicates

and you can trash the iphoto library but it is not recommended

Yes you can delete the iPhoto library - but I suggest you do not - it cuts off your ability to go back if you need or want to

No you do not have duplicates and no you are not using twice the space - iPhoto and Photos share access to the same set of originals so deleting the iphoto library will free up very little space and not change your system speed unless you have other problems like little free space (you need a minimum of 10GB of free disk for normal operations) - see Photos saves disk space by sharing images with your iPhoto or Aperture libraries - Apple Support

LN

No - it is correct  but no matter - since you do not read the responses I will not make any more

Good luck

LN

Graphicstation, If you click on the link provided in LarryHN's original response, you will go to a page on the Apple support site and written by Apple. To save you the trouble of actually going there, I am inserting the text from the page below. You will see that it describes exactly what you are seeing and clearly states that there is only one set of images even though Finder makes it look as though there are two. I have underlined the most relevant sentence.

In the event you don't trust me either, you can go to Duplicate Photo Library with Duplicate Images and see it live for yourself.

Photos saves disk space by sharing images with your iPhoto or Aperture libraries

Learn how Photos stores images when you migrate your iPhoto or Aperture library and saves disk space by sharing images.

When you migrate a photo library from iPhoto or Aperture, the Photos app creates a new library structure but doesn't duplicate your images. Instead, Photos saves disk space by creating links to the original and preview versions of your images.

When Finder reports the file size of your Photos library, it includes all your originals and previews. It may look like your remaining iPhoto or Aperture library is taking up twice the space on your hard drive, but it isn't—your images exist only in one location, even though you may have more than one photo library.

After you migrate your iPhoto or Aperture library to Photos, you might feel tempted to delete your original iPhoto or Aperture library. Because the migrated library takes little additional space, you don't need to delete the original library.

You can still use your original photo library with iPhoto 9.6.1 and Aperture 3.6 after you've migrated it to Photos. Any changes you make in iPhoto or Aperture after you migrate to Photos, like image edits or album changes, will be visible only in iPhoto or Aperture.

Last Modified: Jun 1, 2015

OK, I did misunderstand what you were saying, but after seeing the Finder windows you posted, I went to look at my own libraries, and, lo and behold, when I upgraded to Yosemite it apparently did the same thing to me. You're clearly using a much larger disk than I am. I have an old MacBook Pro with a 250 Mbyte drive and I pay fairly close attention to amount of free space I have on board. Free space varies between 40 and 50 Gig so I believe I would have noticed if my 20 Gbyte library had been duplicated.

However, I now think I have a parallel situation to yours and I will look into what's going on on my machine and get back to you.

I won't be able to get back to this until later in the day tomorrow, but I'll go in through the Terminal window and see if I an figure out how they're managing the file referencing in my case.