My only quible with this is that it really isn't that clear which two towers are being refered to in the title. In the book there are actually 5 towers (3 held by the bad guys, 2 by the good guys) and you can make a pretty compelling argument for any combination. I've always leaned towards Orthanc and Mordor myself but it's not that cut and dry, my second favorite interpretation are the tower at Helms Deep and Minas Tirith, the sites of the two big refusal to yield battles (one fought in this book, the other prepared for in this book and fought in the next). Then there's also the Witch King's tower (moved to the third movie) which the ring passes close by which couples nicely with either Orthanc (both towers were once owned by the good guys and built for defense) or Mordor, plus a few other combos of the five.
But for purposes of this essay Suaron's and Sauroman's homes work best, and from that assumption it's otherwise spot on.
The Two Towers in the title of the book do refer to Orthanc, where Saruman resides at Isengard, and to Barad-dur in Mordor where Sauron is, so your leaning is correct. The title refers to the the alliance between Saruman and Sauron.