Like all the commentors are stating, the tasks you are trying to complete feel a bit much for an ajax call.
I'm guessing you regularly update the Excel file and need to update it to WP?
Is it ok if I was to return the ajax call after each insert-step and then start a new one.
Sure that's an option, i've build many ajax batch loaders for collecting large data sets and sending mail. This way you also circumvent PHP script timeouts.