is it possible to delete all the samsung pre installed apps that you will never use ?
eg, klms agent, knox, knox notifications manager, knox store, samsung learning, samsung in-app purchase, the list is endless.

Believe you can, but only if you root the device. Subsequent versions of Samsung phones has seen the number of pre installed apps, pared back. Even the S6 has pre installed apps which, though you can disable, you can't remove unless you root / install another OS.

Check xda for more details.