Well I think it is not realistic at all, unless possibly I was talking to someone on the moon. I do not really understand why this in particular would be chosen for such a purpose. It already takes longer to read the lengthier passages, what with scrolling and all, that it would to hear it said, for me at least. Then again I am not certain we are talking about the same thing. In every case where the npc has something to say that is not just repeating one of his "what are you talking about" sentences it takes at least 5 seconds for him to respond. The longer his response is the longer it takes for him to start responding. If this is an intentional effect perhaps it could be user configurable because I, for one, would much prefer to keep the npc waiting for my reply than to wait for the npc to finish what he is saying. As far as breaking up what the npc is saying goes it is not a bad thing but I think it would be better accomplished with blank line feeds or lines with just one dot so that the player can know there is more coming.
Several times I have had it happen where the npc has refused my offer of help only to reconsider after I have typed in a query about another thing he had to say and have him expecting a yes or no answer. Let me try to be clear here, his reconsidering was not due to my further queries, he was programmed to have the afterthought in answer to the original "Can I help you."
I am all for trying new things to see if they work, I do not think this works and hope the consensus will come around to my view before too long.