Vim itself is very fast. But it turns to be slow after enabling some plugins. How to find which plugin leads the slowness of Vim?
You may use the profiling mechanisms in Vim. Please check a tutorial on profiling Vim.
For profiling Vim startup:
vim --startuptime profile.log
For profiling certain actions in Vim:
:profile start profile.log :profile func * :profile file *
do actions here
:profile pause :wq