The Edge Transport role is for SMTP only, so that you can have an internet-exposed host performing mail filtering and scanning without the message reaching your actual Exchange org.
Bluntly it sounds like your entire deployment is woefully under-spec: 2500 mailboxes and you're not even providing site redundancy via a DAG. It's not ok.
You should be using the Reference Architecture for a deployment this size: 4 servers, not virtualised, in a 2+2 configuration. A GeoIP service to direct client connectivity to the nearest site, and hardware load balancers or virtual load balancer appliances to manage HTTPS across the 2 hosts in each site. Outlook should all be using cached mode as well. Each DB should be hosted on all 4 servers in the DAG, with 1 copy lagged for recovery purposes.
If you just need to fix things right now then yes, adding another host in so that the host hosting the DBs just ends up doing DB stuff and client connectivity is offloaded to a new host might help a bit. If you're not already using cached mode on as many Outlook clients as possible, fix that too as that is a massive performance drain.
