I ask because so many businesses still use 6.5 instead of w10m.
That's likely because of old specialized hardware like barcode scanners and such that haven't been replaced because they still work. Also its not like they're used for normal functionality.
If I were to compare 6.5 to a modern smartphone (and I have tried to use one recently, albeit it was in Spanish), W10M would blow it away in general design, animations, web browsing, messaging, email, beauty, cloud syncing, phone calls, talking to modern services etc.
Although of course, WM6.5 has a lot of odd features W10M doesn't have but does it matter to the average user? Probably not.
You could live with it though, like it'll do the basic stuff. I could probably barely scoot by with WM6.1 or so.