First, the client is programmed in Java which is slow due to the virtual machine architecture. Second, the applet displays quite a lot of graphics. This is a choice by me. Turn off the graphics and it will run faster. Also, the java application that does the same work without any graphics is available.
Perhaps it is a relief for you to know that, by using the combined effort of hundreds of thousands of computers connected to the internet the slowness of Java could be of minor importance.