Commands can't fire in the "middle" of a round of melee. So "1.5" will always be rounded up to "2". The main difference being that you'll beat the other guy to the next command if both of you are spamming and he lagged himself for "2 rounds" at the same time you lagged yourself for "1.5".

Given what I see when fighting mobs, though, where I can trip again on the very next round after a missed trip, I don't understand how the lag could be "1.5 rounds". Seems like it has to be "1 round" or something slightly less than that.