Multiple Domains In Active Directory

I have connected 19 domains as data sources within Power BI Desktop. I then merged all 19 queries into one table. Once that was completed I then extracted the data i needed and deleted out the columns not needed on the merged table. However, when i go to refresh or change this merged table query it takes over an hour to do so. It is currently pulling roughly 70k rows. 

Is there a way to pull Active directory data from 19 domains and merge that data into a single table for reporting. I believe there is some testing on the gateway refresh of active directory but wanted input on how to speed up this data refresh in this combined data.