I am running Windows Vista 64-bit in VMware Workstation 16.0 and the performance is quite bad. Aero works, but the system lags a lot and it automatically switches back to the basic theme. Windows Vista 32-bit and Windows 7 64-bit both work very smoothly and fast on a similar VM. I have tried Virtualbox, but same results.
i've had this problem before and it seems that vmware 16 has stopped driver support for vista, try changing hardware compatibility to vmware workstation 15 and use the latest driver that supports vista and you should be fine. if you look at taskmgr, you can see dwm.exe seems to be having a memory leak in vmware 16 for some reason whether you are doing something or not.
i think hes already using that because vmware tools 16 gives an error message when installing on vista telling you its last supported os is now win7 sp1. he just needs to change hardware compatibility to vmware 15, he doesnt have to install vmware workstation 15 and ditch vmware workstation 16.