You're kidding right?
The Watchtower moved into Brooklyn around 1908. I don't know how much each building was, but to put it in comparison, a home in Brooklyn around that time cost $10,000. The Brooklyn Bridge itself cost about $15 million to build from scratch.
Believe me, those properties were paid off decades ago. A stingy organization like the WT organization would not be paying interest with money laying around and available to pay off the properties.