Rman DUPLICATE from active database seems very slow

Hi,

I am doing a duplicate database from active database and creating standby .But it seems rman duplicate is very slow .

2.5TB is the source database size and I am doing it from 12.1 to 19c.

It is a cluster database with 2 nodes RAC. I am using almost 12 channels for this.

Below command I have used . Can someone please suggest me ? what to do

run {

allocate channel prmy1 type disk;

allocate channel prmy2 type disk;

allocate channel prmy3 type disk;

allocate channel prmy4 type disk;

allocate channel prmy5 type disk;

allocate channel prmy6 type disk;

allocate channel prmy7 type disk;

allocate channel prmy8 type disk;