Exchange 2013 - How to count number of connection to server

Hi all,

In my environment, I have 2 Exchange Server 2013 : ex01(Mailbox + Client Access Roles) , ex02(Mailbox + Client Access Roles). Database Availability Group : DAG01 including 2 members ex01 & ex02. I have 3 mailbox databases : mb01, mb02, mb03

               ex01                                 ex02
mb01      mounted                           healthy
mb02      healthy                             mounted
mb02      healthy                             mounted

We have about 400 mailboxes , 300+ users online simultaneously, my users access to their mailbox by using MS Outlook, OWA, Smart phone ... How can I count number of client connection to each Exchange server ?
Each server has 16GB RAM, they always use 95%+ capacity of physical memory, we will have more users in tomorrow so I want to know if we need to extend memory.

Thanks.