Are Farro (Triticum dicoccum) and Spelta (Triticum spelta) interchangeable?
According to Heidi Julavits' in the New York Times Sunday Magazine, the grains are very different in their cooking properties, even though they are both members of the wheat family, and despite claims that they can be used in the same recipes:


  Farro cooks in about 45 minutes; we cooked our spelt for four hours,
  and even then the result was extremely al dente. We threw in multiple
  sticks of butter, gallons of stock and $13 worth of grated Parmesan,
  but the spelt remained stoically flavor-impervious.


You should look for recipes specifically for Spelt, if this is what you have available.