Running vagrant ssh
can be slow because it boots up a ruby process, does a bunch of analysis to determine your ssh parameters, and then actually invokes the command. If you want a faster login, try the following:
# Compute the ssh parameters, append them to your global ssh config file
# The --host parameter specifies what you want the vagrant machine to be called
vagrant ssh-config --host vagrant >> ~/.ssh/config
# Now just ssh into that machine directly
ssh vagrant