Does RAM Come Into The Container vs VM Decision?
the benefit of a container starting up fast but they don't talk about heavyweight applications.

yes and no. The container only contains the app and runtime (e.g. JVM), but the app and runtime starts up with the same speed as when running on a VM. But a VM usually takes longer time to create and start since you also have to boot the operating system. So it depends on how you compare.
Running an app in a container does not do your app startup faster.

For this question I would like to know whether the RAM requirements of the processes running within them are a consideration when comparing VMs to Containers, or is there no difference between the two?

The app will use the same amount of resources when run as a container as on VM. But with containers it is easier to manage multiple instances - so you could consider that - this is usually done to achieve better availability and zero downtime deployments - however your app need to be stateless if you consider scaling out to multiple instances.