I need iPhoto back

I had a large iPhoto library and have been using iPhoto for 6 years with great success. Unfortunately, my library has been moved to Photos (which I hate!) and now my Mac is running so slow, it's practically useless. I want iPhoto back! The iPhoto app still shows in my Applications list but has a grey circle with a line through it - apparently disabled.

I've tried the recommended fix - delete the iPhoto app in Applications and reinstall it from the App store (under Purchases) - but I get an error message which says "this version of iPhoto is not available in the US market."

I'm currently running OS X 10.10.4. Is there any way to get iPhoto back? Please help. Thank you.