The T-140 Angara cameras render at a very very low fps - lower than normal. This applies to both the regular and commander versions of this tank.
Regardless of seat used (Driver, Gunner, Commander) - all the screens render at <5 fps, which makes using the internal view difficult for players. I compared by getting into the T-100 Varsuk as both driver and commander, and the fps for the PiP cameras is a stead 30.
On first impression, this seems to be a performance issue when multiple PiP cameras are rendering in the same space at the same time (which is the unique case with the T-140). However I noticed this issue also occurs in the MBT-52 KUMA PiP cameras as both Driver/Commander (And here there is only a single camera per viewing space).