If your internet slows to a crawl after adding a VPN connection then it is most likely because all internet traffic is being routed via the default gateway on the VPN connection. Change this via:-
Control Panel/Network and Sharing Center/Change Adapter Settings/<Your VPN Connection>/Properties/Networking/Internet Protocol Version 4 (TCP/IPv4)/Properties/Advanced – Untick Use Default Gateway on Remote Network. (You may also have to change the same setting for TCP/IPv6). Restart the connection. This solution works for connecting Outlook to Exchange Server on the remote network.