Can't import the XML data

The import depends on the speed of your internet connection and on the speed of your server. If you receive errors or the import is incomplete, probably you have an hosting issue. The best way is contact your hosting provider asking to increase the memory limit, the upload file size, etc. This is not a real WordPress problem and it's not related to the theme and to the plugins installed. It simply happens because you have some limits on your host environment.

More info about this problem here: http://www.tjkelly.com/blog/wordpress-import-failed-how-to-fix-it/.

Alternatively, don't check the option "Download and import file attachments" during the import. But you will not import the images in this case.