The article isn't using the graphs to talk about a difference between 2015 and 2017, but about the overall level, so it would indeed be surprising if there had been a large change between those years.

But there are several demographic variables that show substantial differences between groups (and sometimes over longer timescales within a group), so I think it would be more enlightening to look at all of them, rather than letting someone pick their preferred comparison and then trying to argue with that.