DMS latency

To answer your question simply, DMS is not a real-time replication engine. If you look at the settings for change management in DMS, without BatchApply turned on, DMS will collect transactions from the source database every second. It will attempt to collect the minimum number of transactions for a 1 second period before it applies those transactions to the target database.

https://docs.aws.amazon.com/dms/latest/userguide/CHAP_Tasks.CustomizingTasks.TaskSettings.ChangeProcessingTuning.html

It is also possible for DMS to gather changes from the source DB faster than it can write them to the target DB. It is also possible for these "buffered" transactions to fill the DMS instance memory therefore being written to disk. In these cases, latency will be impacted.

There are many options for tuning DMS based on the customer requirements, so if we look at the specific requirements for the customer's use case, then it might be viable option. However, simply asking for "real-time" replication is not enough to conclude that DMS is or isn't the right solution for them.

Minimum achievable latency depends on the use case and the DMS settings the customer is using for the use case.

Task Settings for DMS

I hope this helps!