Not clear when you say load system database into ASE 16.
If it is a new host + new instance then you will need to create the new RSSD (at least a shell for the load) with matching device sizes.
If it is in place upgrade from 15.7 to 16 then there is no need to load any system databases.
RSSD will get upgraded in the process.
As Mark has given an excellent and detailed feedback make sure that replication pipeline is shut off during the RSSD upgrade. And operation sequence is followed as suggested.
HTH
Avinash