You almost always want to pair lsof with -n, as by default, it (slowly) lists a bunch of things that require name resolution.

$ time lsof >/dev/null

real    2m12.352s
user    0m0.499s
sys     0m1.217s
$ time lsof -n >/dev/null

real    0m1.600s
user    0m0.523s
sys     0m1.029s
$