The Taj Mahal was also built under the same ruler, Shah Jahan, and at about the same time. The wiki entry for the Taj Mahal gives us an idea of the values involved then, and now:
The Taj Mahal complex is believed to have been completed in its
entirety in 1653 at a cost estimated at the time to be around 32
million rupees, which in 2015 would be approximately 52.8 billion
rupees (US$827 million).
If my math works out, at the above mentioned conversion rate I get 900,000 rupees then= 1,485,000,000 rupees today, or $22,985,839.80 US dollars, so less then the $1.5 billion mentioned in the question.