I have two sets of wheels, 15" on all season tyres and 16" on summer tyres. TBH I dont notice that much difference on rough roads that cant be explained by different brands of tyre, rather than side wall height etc. I dont rely on my tyres to 'cope' with potholes. I either avoid them, or drive through them extremely carefully and slowly.
15" wheels have tyres with higher side walls, which may give more resilience and a better ride on rougher roads. Maybe a slight advantage if you push your luck with potholes. It could be argued that this better ride may be deceptive, and encourage you to take potholes less seriously and drive a bit faster. Which soon cancels out any advantage. I have noticed that in India and Eastern Europe its often the off road vehicles, and luxury vehicles that suffer tyre and suspension damage more often than modest hatchbacks.And much more expensive to repair. Their drivers assume they are immune from potholes and drive too fast. Impact damage increases by the square of velocity. You hit a pothole 4 x as hard at 10mph than you do at 5mph.
Forget any notion that 16" wheels are larger diameter , and can span or exit a pothole more easily. The overall rolling circumference is near enough the same on 14",15" 16" ,17" inch or 18".due to tyre profile changes. 17 and 18" wheels require increasingly low profile tyres that makes the tyre and wheel more susceptible to sharp strike damage, but the problem is less on 16".
If I could chose one size it would be 15", the tyres can be significantly cheaper if one does get damaged. 16" wouldnt entice me to upgrade trim level unless it was a significant improvment in appearence.