Stock rom lited optimized – samsung j2 2015 Sm200m 5.1.1
Samsung Galaxy J2 comes with Lollipop version as a default OS. Stock firmware is used to repair Bricked mobiles. Rooted mobile can be flashed using Flashify app. If you flash using ODIN method, you will lose Root access. Lollipop has a lot of features, and Performance Improvement compares with the KitKat version. If you consider performance, You should root your mobile and flash Custom ROM. But, If you are a regular user, you can flash the latest firmware to stay with Security patch.