cannot sync photos to iPad from iMac with new Photos app. Prompt says it will delete all other photos. Don't want to use the Cloud.

I have too many photos to put on the Cloud and don't really want most of them on there anyway for privacy reasons. Previously, I could sync photos to my iPad from iPhoto through iTunes. However, now, with the "Photos" app, when I attempt to sync the photos by hitting the "apply" button, I get a window that says it will erase all those photos elsewhere. All I want to do is to add some photos to my Mini, and after 1.5 hours trying to do so, I'm disgusted that it's so difficult. Anybody have any ideas? A Google search told me nothing.