[Wolfhelm]

I think you are suffering from a common misunderstanding to tell you the truth.

Speedtest's website shows you your transfer speed in terms of kbps (kilobits per second), however, when you download something with Internet Exploder/Firefox/most other applications it tells you your download speed in terms of kBps (kiloBytes per second).

There is roughly 8 kilobits to a kilobyte, so 1200 kilobits = 150 kBps, or exactly what your download speed is.