iTerm2 is very slow when start

for i in $(seq 1 10); do /usr/bin/time /bin/zsh -i -c exit; done
        6.75 real         4.22 user         1.99 sys
        6.68 real         4.26 user         1.83 sys
        6.02 real         4.13 user         1.79 sys
        5.81 real         4.01 user         1.72 sys
        5.81 real         4.01 user         1.73 sys
        6.11 real         4.22 user         1.82 sys
        6.55 real         4.18 user         1.75 sys
        6.57 real         4.21 user         1.75 sys
        6.58 real         4.15 user         1.75 sys
        6.42 real         4.05 user         1.74 sys