Your line speed to the internet will effect this as much as the server, this would be from traffic jam. You might even consider using a third party service to host the database. If the user connection is dropping because of signal, then the only choice you would have is syncing. Here is a link to a free syncing app which does require Filemaker server. http://www.fmeasysync.com/
I have my DB hosted by a third party company, Datatrium.com.
I do not have filemaker server bc of the high price of having concurrent connections.
the dropped/slow connections are really becoming an issue. Im also getting damaged files every month or so. I have to pull if off the server recover it, then re-upload.see link