Interesting, I had not seen that link. From what I read here and in other sites, the T99 Armata is a universal chassis of specially-designed steel, and that for the purposed variants (MBT, IFV, etc.) the real similarities will be in active protection and advanced armor accessories. In other words, the T15 (IFV variant) would not for the most part have equivalent thickness core hull armor as the T14 (MBT variant), but would have similar optic and APS, and crucially, would be able to layer on the new grade of composite and reactive armors developed specifically for the T14/T99, and the cancelled T95 project.

In other words, sure, it will have very good overall protection compared to all other armor in its class, but if actually hit in any part by some anti-tank projectile would not have as good a chance at resisting penetration as the MBT variant in a homotopic portion.