This is not obvious at all. Lowered compared to what? None of us know how fast armies will move in I:R yet.If a battle has to last for ingame-weeks (instead of at most a few ingame-days), so that the player has enough real-time to react, then it's obvious, that the ingame-movement-speed of armies has to be lowered accordingly^^
Are you trying to do some zen thing here, wanting to lower I:R army movement speed below what is currently implemented in the alpha that none of us have seen, based on the assumption that if PDS follows the same design paradigms they have so far, it will in the released game be faster than you believe you will prefer?
In every PDS game the movement speed of armies is the result of balancing several competing factors. Some that argue in favour of faster movement, some slower. I expect the same to be the case for I:R, and that there's nothing obvious dictating what the speed should be.