@hund two possibilities for sharing files of any size in a peer to peer fashion with some degree of privacy and no software installation...
@hund Onion share? Do they have brave installed? What about making a bit torrent? Maybe a reverse web proxy?
@hund A Blu-Ray or flash drive + your local mail service.
At this size you just NEED some software. If on Linux I would recommend doing this via rsync and ssh, but one of the two then needs to be comfortable setting up a guest SSH account or run the rsync service itself (ugh). Or HTTP(S) via Apache, and the receiving side uses curl with automatic resuming (there is a flag for that).
@hund tell them that opening any website is essentially the same as to install a new piece of software nowadays.
That could be a reason for them to rethink the way they do things.
@hund There are various file sharing websites, and my favorite is probably gofile.io
But if it's an actually sensitive file i'd use a proper cloud storage like Nextcloud
@hund split into 8 segments using split(1) with the -b option, upload to https://upload.disroot.org/ or some other open Lufi instance, let the recipient recreate the original 15 GB file using cat(1). (If the recipient is on a system unable to join or concatenate data... What are they using that computer for?)
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