What Miriam neglected to mention is that she lucked into a VERY early 15.. Only the very earliest ones were made with the cast iron face you see this one have. The castings are very similar to it's predecessors.
I would imagine the cleaning process Glenn outlines would be more than enough for this machine. (Not the shellac treatment one) This machine has a REALLY nice look to it and the simple cleaner Glenn shared would do wonders to this machine.
Great job! Now you just need a matching "puzzle box"