2015 was the year that Apple moved to NVMe SSDs, so they are bound to feel much more snappy than spinning rust disks, regardless of the file system involved.
Except for their desktops models, the base models of even the 5K iMac still ship with a Fusion Drive, and we only just got support for APFS on those configurations with macOS 10.14. As the base models are typically all authorized Apple Resellers and pop up stores get they must sell a bunch of those especially in regions where there aren’t a lot of Apple Stores (and where people don’t want to pay full price for a year old system).
They are going to need to support and perform well on non-SSD systems for quite a while.
They are going to need to support and perform well on non-SSD systems for quite a while.