How do I lower it in VO?

I am not exactly sure what you mean bu sensitivity but does this help? It is possible to increase the size of the null zone in the centre of the joysticks range of movement , this helps by preventing unwanted drift/roll when a stick is not exactly centred - this is achieved throught the joystick setup page in VO -

or, if you run win-blowz like me, you have to manually edit the values in the config.ini.

the trouble with 'sensitivity' on a joystick is that the joystick has limited values.

If you increased the sensitivity on a joystick, there would be wasted movement on the most extreme movements. If you decreased it, the maximum could never be reached.

I wouldn't mind seeing some kind of gradual sensitivity setting, so I can actually tune the fine movments to have a lower sensitivity, but still have my maximum values on extreme movements so I can be quick AND accurate.

OK NOW I understand, kind of like editing the response curve, right smittens?
I don't know how to do this in VO, however, there might possibly be some software that came with your stick that will allow you to do this.