To meet the main goal of being cross-platform, we chose to develop TAXI in Java. This choice implies the use of a strong machine to be comfortable with the editor. It is recommended a 800Mhz processor and at least 256Mb RAM.
The bigger the edited document is, the slower the transformation is, but mainly the rendering of the graphic (depending on the machine).
A workaround to this lack of performance could be to compile TAXI to native code. If you do so, let me know the gain of performance and the problem you might have come across.