“Otorrinonaringologia” (The field of study of Nose, ear and throat doctors) is
the word I remember as the longest in Spanish.
However a quick google search turns out the word “electroencefalografista” (the person who administers electroencephalograms) is longer.
Spanish does not go for too long words, generally, but I strongly suspect the average Spanish word is longer than the average English word (as evidenced by the struggle of early videogame translators to fit the spanish translations in the too short space given to them by the original english speaking programmers)