You can open a console from HMC ssh session instead of slow Java console.
After opening an HMC ssh session, type this command to create a LPAR console login;
mkvterm -m physical_machine_name -p lpar_name
If a previos session is not terminated normally or an another console is open, you can see this message;
"A terminal session is already open for this partition. Only one open session is allowed for a partition. Exiting...."
So we can reset console with this;
rmvterm -m physical_machine_name -p lpar_name