How to downgrade from Android 6.0.1 to 5.1.1

Hello :)

I flashed the latest firmware available for my S6 edge (SM-G925F) : G925FXXU3DPDP (XEF).
I've never used Android 5.1.1 on my phone and I asks to you if downgrade is possible at this point (latest BL I think) and if yes, how ?

Thanks you for your further replies :D
Bye.

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