I have two machines where git bash auto complete is agonizingly slow. When I hit tab, it can take 8 to 10 seconds for the filename to be completed. This only seems to happen
This is a known issue with the stable version of ConEmu.
From the ConEmu page:
Disclaimer #2
If you notice lags while executing batches or commands (from
cmd/git/bash/etc.) just upgrade to latest alpha build or uncheck
option "Inject ConEmuHk". Read Issue 526 for details.