Check the Obvious

First, ensure that you are only replicating those parts of the system that need to be replicated. Some of this is obvious. Don't replicate any table that does not need to be replicated. Check that you are only replicating the columns you need. Replication is very sophisticated and will allow you to replicate both a subset of the columns as well as a subset of the rows.

Replicate Minimum Columns

Once the replication is set up and synchronised, it is only necessary to replicate those parts of the primary system that actually change. You are only replicating those rows and columns that need to be replicated, but you only need to replicate the actual changes. Check that each replication definition is defined using the clause:

create replication definition rep_def_name

with primary