There is 1GB file size limit for uploading to Mediabox PA projects. The amount of files and type do not matter (see Supported File Types solution here:https://mediabox.freshdesk.com/support/solutions/articles/138097-supported-file-types-). Keep in mind that your computer network/company firewall will affect the speed of your upload.
Hint: Excessively large file(s) tend to time out during uploading. If file doesn't upload 100% and is not an extreme file size, chances are the file itself may be invalid/corrupted.