Since derrellgore and I are both using Xcode 6.3.1 and derrellgore reports no crashes, something exists for me that does not exist for derrellgore.
A few days ago, I started a new playground to continue where I left off; no crashes. There is something in my earlier playground that causes Xcode to choke. Certainly, Xcode should be more robust and handle my bad code with more grace.
Right now I am more interested in moving forward than dwelling in the past, but I will try to isolate this when I find the time and report back. In the meantime, I did include the first playground in my bug report to Apple, so maybe the Xcode team will sort it out.