Modules integration using jar or HTTP

We are working on some modules of our application. I was thinking to run the module on another Tomcat server as webapp and integrate the module with application using HTTP. However my Manager is having the view of using the module as jar. He has the point that http calls can have latency associated even on LAN.

My question , is HTTP call is better or integration of module as the jar. I always get to hear about this latency kind of thing on LAN and have no answer for that. Which is better in terms of architecture best practice.