HS-14 had 4 verniers, 1 main nozzle.

HS-15 looks bigger diameter, no verniers, and, as @wslafoy observes, two nozzles.

Notice that blunt shroud/RV.
HS-15 reminds me of the Titan II. 😬 pic.twitter.com/aQxK7PSXMS

— Martin “HEU & Santa” Pfeiffer (@NuclearAnthro) November 29, 2017