This is a tough trajectory to track and predict; the anomaly that was the year 2020 in all of consumer electronics made most tried and tested methods and historical data less relevant and applicable. That said; I voted for the 15-16.4 option. I wouldn't be shocked if it fell below that, but the same goes for reaching its upper numbers (mid-16s). With Europe looking sluggish, market saturation setting in, and the overall realities of a sixth year on the market set in, it's hard to see how anyone can argue it selling in the 20s again this year (or anywhere near that mark).
Let's also consider the fact that there is no magical "mass-market" price point, perceived value rules the day, and hitting a certain price doesn't kickstart insane growth by default.
But, once again, it's shocking to see that jump between 2019 and 2020, that's about a 50% increase yoy! Global sales we're seeing now aren't that slow, it's more that the market is settling into its usual pace and motions, as seen before the pandemic.