we have EVs for almost 15 years now, one would imagine some real world data on battery life was collected already, even if not widely shared

There was and publicly available, although the mainstream press mostly chose to ignore it.

My VW hybrid is just over 10 years. The advertising claimed 28 miles on a charge, but the reality was about 18 maximum, with stop-start somewhat less. After a couple of months when it had calibrated, it settled displaying 21 miles for a full charge. 10 years on, and it still reads 21 miles on a full charge, but the reading is less useful in use. It's common for it to drop from 21 to 15 miles after a mile, but to stay on 1 mile remaining for around 4 miles travelled. But essentially, I don't consider the range to have deteriorated too significantly, it still feels around the same ballpark.

A lot of the original thinking about batteries comes from the Nissan Leaf, introduced in 2009, when they guessed that batteries would probably need replacing after 10 years. However, from the cars that were written off from accidents, they discovered much less battery wear than predicted, and around the time I bought my car, they were suggesting batteries would be around 80% after 10 years and most manufacturers started using that figure. I'm not sure what current estimates are, but I wouldn't be surprised if it was closer to 90% after 10 years.

It's common knowledge amongst owners that range is significantly reduced in cold weather - I'd guess from my use, maybe 20% less range on a cold winter day compared to summer.

And as to why car batteries last so much longer than e.g. phone batteries, I think it's mostly because their charging limits are much more pessimistic. Typically a car charger won't ever charge beyond 90% capacity or discharge below 10%, and this is built into its estimated range (so 0 miles remaining is 10% charge).

Battery chemistries have changed and technology has improved a lot in that time frame. Those 15 year old Nissan Leafs have terrible battery degradation, because they're not liquid cooled (hot = bad) and used batteries that degrade fast (LMO, which autocorrect thinks should be spelled LMAO). Manufacturers learned their lesson and every EV built in the last 5 years is far better on both counts.