I believe IETLS is valid in many countries to validate a certain level of English to become a part of an institution (as a student or employee), but I don´t think it is equivalent to a teaching degree. Educational policies on this topic tend to vary from place to place and change from time to time too, according to changes in the communities and the need to cover teacher´s positions. I think you should contact the Spanish Embassy in your country or find their site on the net and ask them directly.