It sounds like you remote into your office PC, so if this is the case, your office PC is using your company’s connection and the only traffic going through your Home ISP is the VPN and RDP traffic. So no you don’t have to worry about it consuming your download limit.
I disagree. If the VPN connection is made across your home link, the traffic to/from the VPN network will be part of the total traffic on your home link. It will count toward your usage volume.