With both castles, yeah. But a single castle? That's pretty damn big(a single castle that's a couple hundred or so rooms shy from filling up two separate castles)!
All info here: from Neogaf:
Again as it's been stated, Iga developed the original Symphony of the Night with only 20 developers on staff. Also It's a safe guess the budget for SOTN was much smaller then what he has to work with for Bloodstained. Then again development back in 1996 was much less costly then it is today, so there is that to consider.
As for the 1600 Rooms. It's almost as big as the entirety of Symphony of the Night.
Symphony of the Night had a total of 1890 rooms. 942 in the regular castle and 948 in the inverted castle.
There's six squares in the inverted castle that aren't there in the normal castle, which is where the extra 0.6% comes from. (200.6%) as referencing this accuracy map - home.golden.net/~maggi/wbw/2006.html
Now if Bloodstained has a reversed / inverted / mirror Castle. 3200 total would be absolutely massive.
As it stands from a single Castlevania without a secondary castle, Bloodstained would indeed have the largest single Castle on just room count alone.
Source:
http://www.neogaf.com/forum/showthread.php?t=1044304&page=224