How to determine if LTM 1600 can handle decrypting and encrypting for exchange2016

The authoritative answer to this would be to talk to your account team. They can look at your actual traffic (7400 clients could be 74000 connections, potentially) and the ciphers you are using and determine whether this will be a problem for you.

This doesn't sound like a tremendous load, but if you are using a cipher that is not hardware accelerated or are using an exceptionally large key you could run into problems. Also be aware that the 1600 is end of sale and will be end of Software Development next month.