Retrieving data from datasource after close & load in Power Query takes forever

I have a folder with 50+ files. My desired outcome is to combine the files in power query and then include an additional column (by referencing a file via the merge function) in the combined table. 

I have no issues combining the files and adding them to the data model, or using the merge function to pull in values for the additional column. 

The problem comes after I try to "close and load" after having done the merge. I have tested it several times, and have been too impatient to wait it out to determine the exact time. It's always gone beyond 17 minutes. 

Am I doing something incorrectly here? My file is about 1.2 million rows. 

Sanja