I Was Told I Have A 15 Cm Ovarian Cyst

I was told I have a 15 cm ovarian cyst and my OBGYN is sending me to a surgeon to have it removed. I had a ct scan. I asked if doctors could tell from the surface of the cyst if it was cancerous. She said usually. Is that true? Should I be concerned about cancer with the its size and the fact that she wanted to forgo an MRI and get me to a surgeon ASAP?
I 52, by the way.