While there is no formal, built-in solution what you are asking, I would recommend you explore an Okta Org2Org integration. Considering they are both your tenants, you could connect the two for provisioning users & groups.

Configuring Provisioning for Org2Org - This link provides you the step by step instructions. Or this link - Integrate Okta Org2Org with Okta

Keep in mind the following:

• It is really important to ensure that you are not importing from your test tenant (Preview) to your production tenant (Production). You want to ensure this is a one way push from prod to preview so you can test with real data but not impact production operations in any way.
• Second, I would recommend you anonymize the data best you can or not map certain PII to the preview tenant. Alot of customers do not have the same monitoring solutions or security posture established for their test environments, and so you don't want to put real production data in harm's way. Assuming you have a fully identical environment to your production tenant, then this may not be an issue for you.

For SSO, you can always setup an external IdP as well from one tenant to the other. Add a SAML 2.0 IdP

Thanks!