Q: iPhoto and Photos Libraries in picture folder - double data?

Hi

A question related to iPhoto and Photos (iMac Retina 5K, 27-inch, Late 2014, 4 GHz Intel Core i7, OS X 10.10.5):

I imported my iPhotos into Photo a couple of weeks ago to my new Imac. Both the Photo Library and the iPhoto Library are visible in the my picture folder. The iphoto Library gets described as  "Migrated Photo Library", the Photos library as "Photo Library".

The Photos library has 138GB and, I think, must include also my old iPhoto library of 126GB, which I moved a couple of weeks ago. The difference between 138GB and 126 GB = 12 GB is roughly the amount of GBs of photos which I took in the last weeks.

Can I delete the iPhoto Library? Or do I get in trouble? This would help me in terms of freeing storage space, but I am not entirely sure if all photos of iPhoto are alrealdy included in my new Photos Libray?

Thanks!