1) Because each phone has a different used storage :3
2) I forgot to switch off the Power Saving button in S6 (which means its limiting the cpu performance)
3) S6 from this video is already used for a 3-4 months but the Xiaomi Redmi Note 3 is a new device that we just bought it yesterday before this video was uploaded.
But from this Video we can conclude Xiaomi Redmi Note 3 Win the speed test.
From the Specification Xiaomi Redmi Note 3 has faster CPU clock speed