A Microsoft Excel file is rendered slowly in the View File Macro when there are a lot of rows and columns in the file (eg. hundreds). These rows and columns can be empty and Confluence can still have difficulty rendering it.

It's possible to set some parameters to limit the number of rows and columns but these have to be set manually by the author of a page:

{viewxls:name=my spreadsheet.xls|col=2|row=2}

The code above will show the first 3 rows and the first 3 columns.

Please make the macro to limit the number by default if the col and row parameters are not set, eg. 100 columns and rows.

A better way perhaps is to pop a window and inform the user that the numbers of row / column are more than 100, then ask how much they want to resize it to (please limit this as well so they don't shoot themselves in the foot).