I agree 100%,
I often work around this performance issue by doing what Corion suggests.
I'll use the real spreadsheet module to read the data, then export it to a json or yml file
In the test I'll import the json/yml file instead of reading the spreadsheet.
The json/yml import is easily 10x faster than the spreadsheet read even without the debugger


I was just hoping there might be a clever way to skip those steps...
This was really a one off test I was running so I didn't take the time to do the export.