In the past and in the present, having a slow mobile page speed is fine because if your desktop page speed was performing well then you didn’t have to worry about it.
Well, updates to Google’s mobile friendly algorithm can be changing that aspect. The reason for the change is that many of the factors surrounding mobile rankings have to do with desktop pages, not actual mobile pages. That doesn’t make sense does it? Well, Google will be addressing that in the next months to come. What Google hopes will happen is that they count in speed as an actual factor of the mobile friendly algorithm.
If you think about it, it makes sense to apply a factor for the mobile algorithm to be based on mobile pages, that is essentially what it is for. If we merely observe it based only on how it performs on desktop pages. Then are we really addressing the mobile algorithm, if we are going to have a hard time when loading mobile pages? This should definitely be addressed. So at the present moment things are as is, and currently mobile page speeds are not a ranking factor as of yet. They will be in the near future as Google states it is months away, so it is important to address those mobile page speeds now to not get any penalties in the future.