While importing 150 GB file on Amazon RDS, why connection is failing?
It's the file size that's the problem.

Essentially there's a timeout expiring somewhere, the server logs will tell you where.

When the timeout expires, no more data is produced, and after a while with no data the connection gets closed as per normal.

The last time I had to tackle something like this (Which is a long time ago now), I wrote a small program that basically pulled the data out of my server in chunks using various SQL criteria.

This is absolutely NOT the best way of doing it, but when you have a table that's so big and takes so long that things start to time out, it's one of the only ways I found to make it work.

The other approach you have is to use an ETL tool such as Pentaho and do a server to server transfer, again using a custom query to do it a chunk at a time.

If you MUST do it using PSQL, then try to break it up.  Instead of one massive 150gb file, try doing the xfer a table at a time or similar.

Also, think about local resources.  You might get better traction if for example, you can dump the file to a server where you have file system access that's inside amazons network, such as an AWS instance.  If you have a local resource, set up an AT job, dump the DB to that instance (optionally G-zipping it in the process) then transfer that file to your PC using a web browser of FTP connection.

Tackling the initial problem head on, your not going to know which approach you have to take until you can figure out why it's timing out.