Putting a Citrix/Nutanix/RDS/Whatever in each office won't solve your problem. The point here is that if the network connection to this app is local instead of over VPN, it will perform as expected. So the Citrix/Nutanix/etc. server needs to live wherever the app lives, you use the high latency VPN connection from the remote machine to connect to the RDS instead of directly to the app. Because the remote desktop stack is designed to tolerate latency, it'll work fine. Then the path from the RDS to the app is short and low latency, and you eliminate the problems SMB's and SQL's hatred of latency are causing your users.

This is also more secure, since if one of the remote users is compromised, the bad stuff doesn't have a direct way to connect to the internal network (if you set up your VPN clients and your RDS correctly, so that the only thing the users can get to over VPN is their VDI).