Take latency numbers while roaming with a HUGE grain of salt when using speedtest.net or similar. Their system will identify you as in another country and pick a server in that country. However TMO's data service terminates in the US so what you've done is add latency to the US + latency back to the speed testing server.

Always best to turn off GPS/location on the phone and this will normally cause speedtest.net to use IP geolocation which will then show you as "being in the US" and get a real latency test.