Also since the VM is optimised for functional programming with no shared memory - it can do tricks you normally cant that help with speed. Like avoid GC in some cases.
Well, yes, the idea that there will be GC pauses and you just cannot get a _consistent_ framerate no matter how hard you try does not sound good. (Disclaimer I currently write games with Unity ;D)
We haven't measured the actual time. I would say the time learning Elixir has not been a hurdle or anyway limiting factor to the projects we are working on.
We basically switched as a company from writing servers in C#/nodejs/python to just Elixir. Did this gradually during end of last year and this spring.
Though I must mention that all of our developers were already familiar with multiple languages. And since we have multiple projects going on we can transfer knowledge easily. So YMMV.
http://elixir-lang.org/getting-started/pattern-matching.html