I think you must be doing something really wrong in your settings for trame or VTK. Normally the defaults are fairly good and should provide a reasonable results. Unless your server is not using the GPU, you should get similar perf as desktop VTK with a capped fps around 30 fps.
interactive_quality has a huge impact for latency but that will only affect the network part of the rendering stream not the server side rendering.
desiredUpdateRate is a different beast as it affect LOD to enable more interactive volume rendering. That is a plain VTK/C++ setting, not a trame one… Also if you are targeting something lower that 30 fps here, you should do the same for trame, otherwise the server will try to render 30 fps and will fail while overloading itself.
Trame should perform similarly and even better than RDP/VNC when properly configured.