Is MongoDB Connections getting too high?
RAM, mainly. Every connection gets a stack allocated, at the size of 1MB. The more connections you have, the more RAM is needed for them and the less RAM is available for keeping indices or the working set of data in RAM.

So with your 19314 connections, roughly 19GB of RAM is used for connections. That's roughly a third of your available RAM – which is too much, from my point of view. What is acceptable has very much to do with your use cases, performance needs and whatnot. Finding out an acceptable RAM utilization is out of scope of an answer and can take many hours of analysis and optimization.