Power BI dataflow very slow

Hi georgec96, 

Another option to consider, if you need all that data, is to use direct query for dataflows.

https://docs.microsoft.com/en-us/power-bi/transform-model/dataflows/dataflows-directquery

I've had to use this recently for a large dataset and it works well. It then gives you the option to build aggregation tables in your model to improve performance but also keep the detailed data when necessary.

https://docs.microsoft.com/en-us/power-bi/transform-model/aggregations-advanced#:~:text=Aggregations%20in%20Power%20BI%20can,the%20aggregated%20level%20in%2Dmemory.

Caveat, this will only work with premium or premium per user as you need to be able to turn on the 'Enhanced compute engine settings' for the Dataflow.

Hope this helps.