One problem with speedtest is it will try to do a test where you are. Since all data is tunneled back to T-Mobile US (via T-Mobile APN's) your terminating point for internet data is actually the US (hence why you avoid the China great firewall and Google defaults to US location). The test will also have nasty high latency as all packets go local network -> T-Mobile US IP network -> Back to local region you are in.

If you turn off ALL location services Speedtest then does IP based location for finding closest server that then gives you a more accurate speed test and general latency info