Oreo introduced features that the J2 never had out of the box:

To make your J2 "better" with Oreo, you typically need to follow this path:

A: To install a full custom ROM like Oreo, yes, you generally need an unlocked bootloader and a custom recovery. Just rooting the stock firmware will not give you Android Oreo.

While newer variants like the ship with Android 8.1 Oreo (Go edition), the older SM-J200G hardware is not officially compatible with these newer operating systems. Technical Limitations & Risks