In some cases, the import file could be more than 50 MB. However, as the import limit is 50 MB, you would not be able to import these files directly. So, you would have to split the content of the file into multiple import files before processing the import.
You would have to split the tickets.xml into multiple files after which you could reduce the file size to less than 50MB. Once the file size is reduced and split into multiple files, you could import these files into Freshdesk.