Upgraded my virtualized (ESXi 5.5) PFsense 2.1.5 a few days ago. It refused to boot until I removed the virtual CD drive, for some reason. I suspected that it was related to the disk driver change, so luckily it was the first ting I tried.
I can happily say, that the new version fixed my issue with CPU usage, where PFsense would report very low numbers (0-10%) while the vCPU was actually running at 85+% according to ESXi. I have no idea whether it's due to a new version of the open-vm-tools package, or BSD10.