I am using Arcmap 10.5 and I have a table stored in a geodatabase so a Geodatabase table with 15 500 000 rows and 8 columns. I joined to this table data from the attribute table of several shapefiles having a common field with the table using the "Add joint" tool. To keep the joins permanent with the original table, I tried to export the table. My problem is that the export process starts but never finishes. I thought it was the number of rows that was the problem but without the joins when I try to re-export the original table under another name it takes 10 minutes. I think that the table refuses to be exported with the joins and I don't understand where the problem is.
How many more columns are appended to the table with the join? And are you really using shapefiles? Is there a particular reason you cannot use a relationship class rather than a permenant join?
Have you created indices on the attributes participating in the join? (ArcToolbox, Data Management Tools, Indexes, Add Attribute Index). I don't think shapefiles and file geodatabases support multiple indices directly, but it still might help.