I don’t think I have the whole picture of what you’re trying to do, but here are some ideas:

Assuming you’re calling a Lambdas function to do the GET, you could have the function return an error if it should retry. You can then configure a retry that gives up after 15 minutes (see https://docs.aws.amazon.com/step-functions/latest/dg/concepts-error-handling.html#error-handling-examples).

Another option could be to use a Choice to interrogate the Lambda function result. It could also use one of the Timestamp comparison operators to determine if it should try again or not (see https://docs.aws.amazon.com/step-functions/latest/dg/amazon-states-language-choice-state.html).