If you don't allow the Otoman empire to be the antagonist faction but a Catholic bishop or Spanish conquerors can appear like the bad guys of the story, then that is double standar.
At risk of veering off-topic, there is, in fact, a fantasy allegory of the Ottoman Empire in the D&D Multiverse: namely, the Hagiarchy of Great Hule, in the World of Mystara. And, for better or worse, Hule is mostly presented as an antagonistic faction, as worshippers of the entropic power of Loki.
Furthermore, Hule has Spanish-based neighbors...the Espan peoples of the Savage Baronies. Each barony represents a different aspect of Hispanic culture:
Torreon: Inspired from Spanish conquistadors, mostly swordsmen for hire and mercenaries. Everybody has Torreoners in their pay.
Narvaez: Inspired from the Spanish Inquisition (knights and priests, early 1600's). A place to avoid for "heretics," non-humans, and wizards.
Saragon: Inspired from Moorish Spain. Also a magiocracy.
Gargona: Mid 1600's Spain, a place for artists and diplomats.
Almarron: Spanish California. Los Angeles at the time of Zorro.
Guadalante: Gauchos of the Argentine pampas.
See: "
Savage Coast Real World Cultural Inspirations"
But that's not what this thread is about.