any idea to retrieve excel range values from background process?

Hi,
let me explain my task briefly, I have one excel spreadsheet which is connected to one external data source and retreiving live data from that and updating it every second.
I want to write one background process (i'm not sure, it can be a macro?) which collets data from my sheet and mail it to a recipient for every 15 mins.
i know, i can achieve this by writing macro within that worksheet.
but i would like to keep it seperate from my workbook, because some time any interruption to my worksheet causes macro stops running.

How to achive this without any interruption? and, that background process can be a macro wriiten in vba? Any help would be greatly appreciated!
Thanks.