Out of interest, what latencies are other users seeing, for what arguments? You can find out (if you have time installed) by changing your _update_ps1 function like this:

function _update_ps1() {
    echo "powerline"
    time PS1="$(your powerline-go command)"
}

I have powerline-go taking 100-200ms, with the command

powerline-go -colorize-hostname -condensed -cwd-mode plain -priority 'root,cwd-path,exit,user,host,ssh,perms,git-branch,jobs,git-status' -error $?

e.g. when cding into a directory with no python environment:

real	0m0.108s
user	0m0.062s
sys	0m0.051s

And when cding into a directory with a python environment:

real	0m0.191s
user	0m0.112s
sys	0m0.096s

It's not much in the grand scheme of things, but it's a bit of a pain given it's added to every command run! I was just wondering whether my experience was typical.