Thanks for your posting and using Aspose.Cells.
Please download and try the latest version:
Aspose.Cells for .NET 8.7.0 and see if it makes any difference and resolves your issue.
Since your excel file is quite large so it will definitely take some amount of time. Please upload your excel file on http://dropbox.com and share a download link with us for evaluation.
Please also share the sample code you are using for our testing. We will look into it and help you asap.