Sorry for the late reply.
I use PostgreSQL as Conquest db engine. I confirm that virtual server mechanism work really well. There was some issue with Orthanc server after it goes out of free space which caused problem with pulling studies from him through Conquest. After reinstalling Orthanc (and increase capacity of disk ;)) everything works correctly.
I have question related with VirtualServer feature. Is it way to tell Conquest to not storing locally studies which are sendt through virtual server? Currently it looks that Horos looking for studies on remote (virtual) server throught Conquest, find them on Orthanc, pulling studies from Orthanc but also those studies remains on Conquest which in my case is not goal and I have to deleting those studies from Conquest and reinitialize db using script in cronjob.