I have Parallels v11.2.1 and am running Windows 10 Pro with decent specs on my iMac 5K 27" with 16 GB memory and Core i5 3.2 GHz. I have played around with the settings way too much and can't seem to get it working 100%. There are some times where my VM works flawlessly, but that only lasts a few seconds. For example, bringing up the start menu is very laggy and can take up to 10 seconds....sometimes it is instant. Opening applications like Google Chrome takes many seconds to a minute. Parallel Tools is installed and is up to date. The VM has real-time optimization turned off, 4 processors, 4 GB memory, 512 MB graphics memory. Any help is appreciated!