How to compress qcow2 to compressed qcow2?

Be aware! Do not forget stop container! Running this commands on running container is strongly prohibited! 

Example:

qemu-img convert  source_not_compressed_qcow2.img -O qcow2 -c  target_compressed_qcow2.img

Before:

ls -la source_not_compressed_qcow2.img
-rw------- 1 root root 1,5G Янв 28 06:37 source_not_compressed_qcow2.img

After:

ls -la target_compressed_qcow2.img
-rw-r--r-- 1 root root 578M Янв 28 06:54 target_compressed_qcow2.img

In my tests qcow2 with compression is very-very-very slow!