I'm having the same issue. Template with zero plugins loaded, cubase 10 closes and opens very slow. If I disable all the outputs of Vienna in vst instruments, it's a little bit better. Activated and disablilng those outputs takes FOREVER. I'm still using VE 5 because of the awful folder organization, which is by vendor and developer instead of the neat folders I created. I got tired of searching in a separate window for program files - vst plugins - Eqs, compressors, etc.
Maybe folder organization will come in version 10 lol.
BTW I loaded an orchestral template with over 200 vienna 7 outputs engaged in cubase, could not use it at all.