There are several factors that influence the speed during rotation. These are your type of processor, available RAM, number of atoms, number of bonds, number of polyhedra.
I cannot do anything about the first two. However you may increase the speed during rotation by switching the display of bonds and polyhedra OFF. This can be done most conveniently by checking the checkbox "economy" under the menu [Mode] . This affects the rotations by mouse dragging and by using cursor keys. After releasing the mouse button or cursor key the original display mode is reestablished.
Of course you may also manually switch off the bonds and polyhedra in the mode menu or by clicking at the corresponding LEDs on the status bar.
You may also choose "thin lines" for bonds and "draw Discs" for atoms, since the drawing is faster then.
If available you may also use a Java Virtual Machine (JVM) other than the Java interpreter in the JDK1.2.
©Sun Microsystems plans to release a JVM called HotSpot which is supposed tu run Java programs much faster. However, Hotspot is not free but a commercial product.