what you see is the lack of performance of tables compared to the same raw contents of a text story with tabs.
There are so many properties additionally in a table cell compared to the ones of formatted text, that the difference you see in performance is no wonder at all.
What you can try is to open the document without a layout window, then place the table with ExtendScript and after this is done give the invisible document a layout window with e.g. doc.windows.add() written in ExtendScript.
Regards, Uwe Laubender ( Adobe Community Professional )