The number of pages in an outbound fax is not the only factor that determines the time it takes to transmit.
The actual size(in bytes) as well as the quality of the originating document influences the transmission time dramatically.
Highly pix-elated files, or files of poor originating quality will take longer to render or not render at all. Pictures and logos in particular.
If the file is damaged or the paper has creases it will also manipulate the transmission time dramatically.
Fax technology interprets any image as series of a black and white dots, a granular image plays a major role in the time taken to transmit and receive.
A standard black and white fax image consists of a grid of pixels at fixed resolutions and image sizes compressed in a particular manner.
The number of pixels in the image depends on the vertical and horizontal resolutions (dpi or pixels/mm) and the size of the image.
The size of the image (in bytes) depends on the image dimensions, resolution, content and the form of data compression used.
Basic fax mode transfers in black and white only and the document is compressed into a series of black and white runs for a single scanned line.
An A4 document is typically scanned at 1145 lines per page if these particular files were mostly made up of black and white lines or dots,
the compression ratio would have been far lower during this transaction.
If this is the case we suggest that you decrease the size of the document(in bytes) or find a better quality version of the originating document.