Java based applications have traditionally been slow over the internet. This is a result of several reasons, including java’s virtual machine and its rendering capablities.
There are several options available to try to speed up java based applications.
Edit the remote host’s java properties.
Slow performance is a known issue when remotely connecting to Java applications using any X Server, not just X-Win32. Graphics performance problems are documented in the Graphics performance whitepaper
http://java.sun.com/products/java-media/2D/perf_graphics.html
The specific section for Remote X displays can be found at
http://java.sun.com/products/java-media/2D/perf_graphics.html#21826
Sun Microsystems has several unsupported properties which it uses to speed up performance.
http://java.sun.com/j2se/1.5.0/docs/guide/2d/flags.html
http://java.sun.com/j2se/1.5.0/docs/guide/2d/flags.html#pmoffscreen