If it needs 2mm, then do it. Just hold the screw up to the drill first and if you can still see some thread either side, you should be fine. If not, try widening the 1.5mm hole if you can. The screw doesn't need a huge amount of grip to push down hard to hold anything in place, just itself. The fact that it's there will stop the machine head turning. If it feels a bit loose in the bigger hole, then a drop of PVA or Titebond glue should hold it a bit more securely.