Parallels is such BS. Every time there is an OS update. The old version is suddenly incompatible and you have to buy a new version. It's reached the point where it is blatantly obvious they design it to be incompatible.
It wouldn't be so bad if Apple didn't make a new version of Mac OS X once a year. I wouldn't be surprised if they released Parallels 12 in one or two months when 10.11 "El Capitan" is released.
Apple's greatest feature is it has programs capable of running Windows. Why even bother with Apple honestly. I'm currently suffering using a macbook air on holidays. It feels like using Windows 3.1 but with less features. Things are unnecessarily difficult and overly complicated. I really wish someone had stolen my wife's mac instead of my cheaper, more powerful, and more intuitive windows laptop. I guess the thief had used a mac before as well.
VirtualBox on OS X has always had the problem (unless they've fixed it recently) that it uses 100% of the Mac's CPU (or at least as many cores as you allocate to the VM) all of the time. I don't know about Parallels, but VMWare Fusion doesn't suffer from this defect. I gave up using VirtualBox on my Mac, and shelled out for Fusion, because I felt it just wan't suitable for the job.