Go Back from Apple Photos to iPhoto is easy...
You do not like Photos from Apple ? Do you wish to come back to iPhoto ? It is really easy with Time Machine. I did it today. It just took 5 hours with my iMac. You just need to go back to a previous version of Mac OS X. The answer is here :
• English version : https://support.apple.com/kb/PH18846?locale=fr_FR&viewlocale=en_US.
• French version : https://support.apple.com/kb/PH18846?locale=fr_FR&viewlocale=fr_FR.
Of course, choose the last version of Mac Os X you saved just BEFORE you passed from iPhoto to Photos.
Cheers
Pier-Yves
iPhoto '11, OS X Yosemite (10.10.3)