M+ Difficulty increase?

I’ve heard that with 8.1.5 m+ difficulty will scale up. I watched a video by preacher gaming about the new reaping affix and in the video he said that the +14 they were attempting on the PTR was equivalent to a +18 or so on live servers. I’ve also been told by people in game that the new cap for the weekly chest will be a +15, similar to how it was near the end of legion.

Does anyone have any information on this? Will +10’s still be the minimum required for your weekly? It doesn’t make sense to me that they would increase the difficulty of the dungeons and simultaneously increase the weekly requirement to a +15.