I've seen this quite often on the 3 mobile network recently. I can have blistering performance for web traffic, speedtest results in the order of 10Mb/s but throttled ssh sessions to the point I can't even use an interactive shell.
Funny thing is on 3 it seems to be a bit region specific. I think perhaps they do something like shuffle web traffic through a transparent proxy and anything else which requires direct access is severely throttled.
It's probably something like that or that ssh traffic just isn't recognised as legitimate so doesn't get some traffic management rule applied.
Generally for public wifi services like that my first step is to run up a VPN and route all my traffic through it as I just don't trust the operators (or the other users). Though that can mean you struggle even more with performance in some cases, most public hotspots do seem to work ok with it.