How to backup photos app on Mac?
Photos has migrated the iPhoto library to the Photos library. Photos no longer reads from or writes to the iPhoto library. You only need to back up the Photos library.

Providing you have no referenced masters in the iPhoto library, it's fine to delete. Keep a backup of it for a while in case anything doesn't work. You can copy all your referenced masters into your Photos library by opening your Photos library, navigating to All Photos, selecting all the photos and choosing File → Consolidate…. If you have any referenced masters, this will copy them into the Photos library, such that all the data is contained within the Photos library.