To me this sends up a couple of thoughts: (1) this sounds like a way to spy on Russia and (2) quite possibly could be technology from Russia (such as hypersonic missiles).
Then I read the speed:
> An object contrast makes it possible to estimate the distance using colourimetric methods. Phantoms are observed in the troposphere at distances up to 10 - 12 km. We estimate their size from 3 to 12 meters and speeds up to 15 km/s.
... that's 33,500 mph ... Re-entry speed from something out of the atmosphere is something like 8km/s; or 19,000 mph. Of course that generates an insane amount of heat and is still half the reportedly measured speed.
TBH it seems like a possible sampling error for the speed calculations. If we assume that to be the case, then it seems likely (if real) that these are some sort of hypersonic test craft / missile system.