https://cloud.google.com/architecture/best-practices-vpc-design#shared-service Cloud VPN is another alternative. Because Cloud VPN establishes reachability through managed IPsec tunnels, it doesn't have the aggregate limits of VPC Network Peering. Cloud VPN uses a VPN Gateway for connectivity and doesn't consider the aggregate resource use of the IPsec peer. The drawbacks of Cloud VPN include increased costs (VPN tunnels and traffic egress), management overhead required to maintain tunnels, and the performance overhead of IPsec.

"Google Cloud VPC Network Peering allows internal IP address connectivity across two Virtual Private Cloud (VPC) networks regardless of whether they belong to the same project or the same organization."
https://cloud.google.com/vpc/docs/vpc-peering
while
"Cloud Interconnect provides low latency, high availability connections that enable you to reliably transfer data between your on-premises and Google Cloud Virtual Private Cloud (VPC) networks."
https://cloud.google.com/network-connectivity/docs/interconnect/concepts/overview and
"HA VPN is a high-availability (HA) Cloud VPN solution that lets you securely connect your on-premises network to your VPC network through an IPsec VPN connection in a single region."
https://cloud.google.com/network-connectivity/docs/vpn/concepts/overview