Q: Huge iPhoto Library File...HELP!

I purchased a new iMac which came with Yosemite and the new Photos App.   I noticed in my Pictures folder two huge files:

1.  Photos Library.photoslibrary 435gb (I assume this is my main library as the date is current)

2.  iPhoto Library.migratedphotolibrary 372gb  

     What is this?   Could this be my old library from old mac that was restored and migrated into new Photos App?

     Can I delete this file if my new Photos library is working fine?