So the root cause of the slowness was not found, it was just circumvented by keeping 3 xterms open and just using hiding/showing them?
In fact, keeping something preloaded and ready to go is quite common, these two examples are off the top of my head:
- The Emacs server way - https://ungleich.ch/u/blog/emacs-server-the-smart-way/
- SSH connection reuse.