Theoretically you should use the calibration 'template', or wall size, that CalCam calculates for your camera-lens. For practically all SLR cameras the optimal wall size is quite big, for example 11 x 7 meters.
In practice, as it is many times not possible to establish the calibration targets of optimal size, you should set-up the targets as big as your office space allows. We have often used targets of about 3m x 2m for all cameras - the images come out somewhat unclear (because of focus in infinity) but the locations for the targets are correct and identifiable for the software. 2m x 1.5m sounds a bit small, especially if you have long focal length lens. You should try to increase the size to the limit that your office space allows.
If you cannot increase, you can try that size, calculate the parameters and analyze the residuals.
You can use the same targets for all cameras. Again, theoretically you should establish a different size field for all camera-lens -combinations, but in practice you can use the same field for all. It will serve you future cameras better if you increase its size to maximum allowable.