I was visiting a friend on Sukhumvit in Bangkok and I live in the Silom area. She had a internet speed of 2 MB and I have 3 MB but her speed was so much faster then mine. I called True customer support but they off course said nothing was wrong and there was nothing I could do about it.
I know this from before it depends on the quality of the lines in the area and how many customers there is this area. 3 or 2 MB is not out from Thailand it is to the True office or to the closest Thai hub.