Best way to Optimize get data from Excel files

Dear all - I am new to PowerBi.

Each month I have a heavy files of Sales report stored under Excel files , consisting of multiple regions per month . Approx. 70MB per files per region.

I used Get dat from Folder in powerbi query and loaded them , however each time it takes about 15->30 min per month.

Each month I have a new folder like that and to append them together would be such a pain.

So I decided to store them separately as table, because each time I append New Data file, they reloaded the old sources as well (yes I tried to uncheck do not refresh = but not working - it still refreshes).

**So with each month under a different table in powerbi, what is the best way to summarize them (for example, Im just looking at Sum of Total Volume for each OutletCode per month. )

1st I create a new table called ASO All (basically total unique outlet IDs) : Distinct( Union (Distnct (outlet code June), distinct (outlet code _July) .etc.)

And then create the relationships from each Monthly sales table to this new table

Then basically dragged the volume from each month to the table.

I know this is not the most efficient way if the number of table are to increase....Any help would be much appreciated .

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