Adding to this, Volta is 15TF and that's not even on 7nm nor is it the Ti (I think) version.
AMD will most likely jump to 17+TF because they will be using 7nm with the gains to boot, this all in 2018.
Do the math of what 7nm/7nm EUV brings from the image I linked in one of my previous post and you have an idea about 2020.
As long as Navi isn't another RX480/580 situation and AMD keep pushing forward computational wise 16TF might not be far off as to what will be in PS5.
In other words 16TF would be low-end by 2020 as they'll be at 20-25TF (that's according to some info I gathered here and there).
If top tier GPUs are 20-25 TF that means a console GPU will be less than half of that. It's been like this since the XB1/PS4. So for a 15 TF console high end GPUs would have to be 30 TF+. I don't even think we'll have that by 2020.