MS SQL Server: Replication Monitor Transactional Replication Publisher Log Reader Agent Latency Too High? Is my Transactional Replication's Publisher's Log Reader Agent Latency too high?
It depends. But from your screenshot it seems like you have small workload with 6 seconds on log reader agent.. 

you can use the below script to check for the latency of your logreader agent:

USE [distribution]
SELECT la.name, delivery_latency / 1000, [time]
--AVG(delivery_latency / 1000) AS delivery_latency_Sec
FROM MSlogreader_history as lh
INNER JOIN MSlogreader_agents as la ON lh.agent_id = la.id
--WHERE la.name = ''
ORDER BY [time] DESC
--GROUP BY la.name


What you can do/check:


check you publisher database t-log. How big is your t-log? How many VLF it got? Make sure your t-log is properly pre-size.
How often you are doing reindexing? This can also bloat your t-log and slow down logreader agent reading your t-log. Read it here. So be careful on your index maintenance.
Do you have large batch processing? (from your screenshot seems like no but be aware of large batch processing as it can also slow down the logreader reader/write thread)
Slow IO latency on publisher db t-log?
blocking/locks on distribution database? (highly unlikely for small workload)


Note that there's no magic number for the log reader agent latency. It is going to be depending on how you maintain your publisher database t-log. It should not be cause of concern IMO.