In this format (pre-2014), this would be the shortest format. However, oldtimer plates can have numbers as low as single digitd, so that plate would be "ZV 1" which would be shorter and some older Irish plates (in the UK gallery on this site) can also be quite short (e.g. "IM 2), so you can get much shorter Irish plates than this format. It just depends on the particular format the plate is.