The speed of data preparation depends on the amount of data you’ve selected. Most data sources preparation takes a few minutes. But sometimes this can take even hours, for example, if there are thousands of rows to be prepared.
To speed up data preparing process:
Apply filters to reduce queried data.
Try removing some fields from your query so that preparing can run faster.
Break up the data source into smaller parts.
If you need assistance with it, please, contact our Support team.