Unfortuntely I don't think that was a 15c, as it hasn't been made in a while. As GP mentioned, there was a batch made in 2012 and that sold out fast.

It was probably the 12c, the financial model, that has been continuously in production since the 80s. Unfortunately, it's much less useful for engineers than the scientific 15c.

I have a recently made 35s sitting on my desk, but I'm really itching to replace with a SwissMicros DM-15L