See, my XS is a 64GB, and I've got about 5.5GB free.
The only time I ran into storage issues was when my WhatsApp media library got full of duplicate photos/videos, so I think 128GB will be fine for me.
However, I'm conscious that the photo and video filesize of the 15 Pro camera is going to be much bigger, so I'm concerned that even if I double the storage from my current phone, it won't actually take that long to fill up the extra space…
Anyone else been in a similar situation when they upgraded from a 12MP-based phone to the 14 Pro?