Calling powershell.exe is extremely slow

Powershell loads and JIT compiles tons, and tons, and tons of stuff. This takes a lot of excessive CPU cycles and disk I/O.

Try using ngen.exe (Native Image Generator) to precompile the assemblies that Powershell loads during startup. Just might improve your startup time.

$FrameworkDir=[Runtime.InteropServices.RuntimeEnvironment]::GetRuntimeDirectory()
$NGENPath = Join-Path $FrameworkDir 'ngen.exe'

[AppDomain]::CurrentDomain.GetAssemblies() |
  Select-Object -ExpandProperty Location |
  ForEach-Object { & $NGENPath """$_""" } 

Read about ngen here.