ffmpeg conversion is very slow – How to optimize it?

I am cropping and splitting a video of size 13476*1500 into 4 parts, below is the filters. The conversion is very very slow! Is there a faster way to convert the videos? please help! And also i want to know if there is an alternative way to do the same job or with handbrake.

ffmpeg -i input.mp4 -filter_complex "[0:v]crop=2691:1200:0:0[out1];[0:v]crop=4036:1200:2691:0[out2];[0:v]crop=2691:1200:6727:0[out3];[0:v]crop=4036:1200:9418:0[out4]" -map [out1] -map 0:a out1.mp4 -map [out2] -map 0:a out2.mp4 -map [out3] -map 0:a out3.mp4 -map [out4] -map 0:a out4.mp4