They do this every time. 

Apple doesn’t discount their products. So it doesn’t make sense to announce a new phone, yet keep the older one selling at the same price. 

They only do this for incremental upgrades though, meaning if the 15 and 16 are basically the same phone, they kill the 15. 

But if the older model was significantly behind, they used to keep them online as a “mid range” model since apple doesn’t make mid range phones.