Moments in Photo are the new Events. There's a way to simulate events in Photos.
When the library was first migrated there was a folder created titled iPhoto Events and all migrated iPhoto Events are represented by an album in the folder. To open the sidebar if it's not open use the Option+Command+S key combination.
When new photos are imported into the Photos library go to the Last Import smart album, select all the photos and use the File ➙ New Album menu option or use the key combination Command+N. Name it as desired. It will appear just above the iPhoto Events folder where you can drag it into the iPhoto Events folder
When you click on the iPhoto Events folder you'll get a simulated iPhoto Events window.
The downside to the simulation is that the Album/Events can only be sorted automatically by Title. But they can be sorted manually. Ask Apple for more sorting options in Photos via https://www.apple.com/feedback/photos.html.
Now if you want to merge Album A into Album B click on Album A in the sidebar. Select all of the photos in A and drag them onto the Album B icon in the sidebar. Check to make sure all of the photos are in Album B and before deleting Album A.