JMeter takes 3 minutes to open 3mb jmx script file

I am using jmeter 5.1.1. When I start jmeter, it opens immediately. But when i try to open my jmx script file having size greater than 3mb, jmeter takes 3 to 4 minutes to open. It opens the small files within short time.

My script has 3 listeners.

Heap size configured is 1 gb. but still its the same issue.

i think it should not take much time just for opening the script.