I realize that I'm not showing very much of it, so that makes it more difficult to identify.
You are correct on several things....
It certainly is a massive church,
it is not in Istanbul and it's obviously not a mosque,
It is in fact Catholic, as you obviously suspected by the statues, etc...
I really enjoy photographing cathedrals, along with all the rich ornamentation and elaqborate art and other decor.
I'll give it some time before giving any clues, if nobody guesses it.