I think it is very unlikely that you'll get a 10x speedup in Shiny app load times by precompiling the code. The R byte code compiler in general does not speed things up by that much. I realize that you said you got a 20x speedup in your code, but that only happens in unusual cases. Also, in the vast majority of Shiny applications, most of the processing in startup is not spent in the application code you wrote, but in functions that your application calls, and (with recent versions of R), that code will generally be already compiled.
In recent versions of R, the JIT compiler is enabled by default, and a function is compiled (I believe) the second time it is called. When you call reactive(), observe(), or a render function like renderPlot(), it creates a function. There currently isn't a way to tell Shiny to compile those objects/functions when they're created.
Have you tried using profvis to profile your code? It is very helpful for finding bottlenecks.