It can be treated but the area is too large to numb so the pain will be an issue. Laser tattoo removal hurts because any laser that can remove a tattoo is by definition very powerful. In my office we inject every patient with local anesthesia. You I couldn't inject because it would take so much local that you would get toxic. So unless you have a very high pain tolerance I would deem this untreatable.
No matter what Q switched laser is used, it is not likely you will be able to loose the entire tattoo. Also, it is so large that you will probably not be able to tolerate full arm treatments. It would need to be done in segments. Lightening this enough to be covered effectively will take a number of years and be very expensive.