Are you downloading an XSLX file or a CSV file?
If it's XSLX I'd use the ImportExcel powershell module. But I don't understand what you mean when you say you want to remove the "A - AB". Aren't those the column names?
If it's a CSV file and you want to remove the column headers and the first 15 rows it's probably as easy as:
get-content downloadedfile | Select-Object -Skip 16 | Out-File newfile
. . . and then remove the downloaded file.