Mediator Heavy load

We must process large message in Mediator (up to 100Mb). But we have an out of memory exception in Tomcat.
What is the maximum message limit for Mediator/Tomcat? How can we configure it properly so it can process large message. We have already set Java -Xmx to 1536Mb for Mediator Java process, 2048 for the factory and 1546 for Tomcat.

Does some body experienced the behaviour of Mediator with heavy load (log, linear, expenantial,…)?