Traffic Volume Consideration: The traffic volume between the VPCs (50 TB per month and increasing) justifies the use of transit gateways, which are designed for scalable, high-throughput interconnectivity. A VPC peering connection would not scale as efficiently for this traffic volume.

On-Premises Connectivity: Establishing VPN connections from the on-premises firewall to the transit gateways ensures secure connectivity between the on-premises data center and both VPCs.

Transit Gateway Peering: Creating a peering connection between the transit gateways allows for efficient inter-Region communication between the VPCs without routing through the on-premises data center, reducing latency and costs.

Cost Efficiency: Transit gateway peering provides a cost-effective solution for large inter-Region traffic volumes compared to alternatives like routing all traffic through the on-premises data center, which would incur higher egress costs and potentially create a bottleneck.