Replicating to an in-memory database may not be faster than replicating to a relaxed durability database. DML on in-memory databases depends on several factors. See the Adaptive Server Enterprise In-Memory Database Users Guide for more information.
In addition, there is no difference in performance when replicating to an in-memory or relaxed durability database compared to replication between primary and replicate databases which are traditional full durability disk-resident databases.
