FFMPEG: Streaming over UDP over Wide Area Network
Unless you are on a network that supports multi-cast, the host computer needs to have sufficient bandwidth to send the video data independently to every single viewer.  If you have multiple viewers, this will rapidly overwhelm any slow connection (and your connection, even on the LAN, is exceptionally slow).

What you need is a content delivery network or at least a media server with a sufficiently fast upload speed to feed the desired number of clients.  Your host would then upload to the media server or CDN and the clients would connect to the media server or CDN to get the relayed stream.