I decided to look up allot of pics of the t-14 and other BPM's just out of curiosity, ANS Kamas P81 is right on the money about the proportions.
You can get a better idea of how big the T-14 is from the pics from the parade day premier where you can see the commander and driver sitting near the turret.
Furthermore, the more I look at the Reddit pic, the more things look missing. All the angels are right but the certain details are missing, the main gun looks completely stationary and the rack/pegs/whatever for the PK bi-pod are kinda useless for actual combat. If it's photo shop, amazing work. Otherwise I can only think it was a proof of concept mock up or some sort of prop mock up prior to the actual conflict as there are no time stamps.