Here is the latest GemFire 9.15.2: https://network.tanzu.vmware.com/products/pivotal-gemfire/#/releases/1161578 You can get them from here.
Here is the latest GemFire 9.10.16: https://network.tanzu.vmware.com/products/pivotal-gemfire/#/releases/1131946
I realize that this may not be the exact deliverable you are wanting. There is no GEODE now. Please use the term GemFire going forward. You are also correct that if using a 9.15.x client, you MUST have a 9.15.x server. Server side must always be the same or newer version.