I've installed the sample data set from Data management subarea of the sitemap several times, yes indeed it used to be faster in the past but it had never taken me days to install.
I believe your organization might have some problems with this data import and in order for us to be able to check it for the affected organization, as we need to be compliant with our security policies, I would recommend to raise a ticket for this issue providing in it the following details in the ticket:
- organization URL
- the timestamp, the day and the timezone when you initially trigger this process
- a confirmation about the steps you had taken
- a short check against the Accounts entity in order to see if the A. Datum one has been already created and when, if I'm not mistaking that's the first one we create.