Optimizing data for faster refresh / faster process by reducing column size

Hello,

I have one question, as I am getting the following error when I schedule/manually refresh my data:

The amount of uncompressed data on the gateway client has exceeded the limit of 10 GB for a single table. 

If I have one table in SQL which is the data is something like: TAT30495, so being a nvarchar in the table definition.
If import the data as it is, but later in Powerquery I transform it into just the numbers after TAT and then I change the column to integer.. will this help me reduce the size of the column in my model, or should I do this before bringing the data into PowerBI?

I have this model in Import mode, but I could ask the same question for SSAS.
If I need to do it before on SQL server, or if using a custom Select statement (or even powerquery) to erase the characters and later in the model change this to a int column.

Best Regards!