I think they would say that technically the capacity is there, they are just using it.
It is annoying though. They should just sell it as a 15GB drive.
> I dare say that "actual storage less" (and other equivalent phrases) are now past the point of covering for the discrepancy.
I think the original reason for that disclaimer was due to filesystem formatting, not for the GB -> GiB discrepancy or providing less usable bytes on the block device than advertised.
5%+ of missing capacity is definitely large enough for the actual expected capacity to be used for marketing.
This is also something that should find its way into smartphones. Samsung's are notorious for using significant amounts of the advertised storage for bundled marketing apps that cannot be removed.