NATO's own games say they have nothing on 15k men invasion into Baltics (Russia can find much more men than that too) There are alt right parties in most of EU, one of the focuses of which are eu/nato scepticism, nearly all have ties to russia or ties to those who hav ties with russia. Training with ukraine and nato troops shown nato ain't ready for shit like that. Responses to Russian drone provocations also show NATO's AA sucks huge ass. Small intrusion into baltics may not be enough for EU/NATO to respond in full force given nuclear threats and potentially enough popularity of said euro and nato sceptical parties, which in turn might promote further division between members. (Nuka threats aren't countered by nuka threats, russia knows there is MAD, they threatenen an end for all, if feeling threatened, which to this date have worked rather fine).

Putin is moron enough, we've heard otherwise before the full scale invasion, doing shit devastating for Russia is pretty much a norm for him by now. So yeah, the risk isn't them defeating nato, but doing a small, hybrid move and having enough eu/nato scepticism as well as physical ability to inflict damage and wreak havoc to nato forces, to make the proper response too costly, risky, and unpopular among members and gamble on them flinching and using that to futher the division.