NO NAT requires 15.3+, so while your 15.42 is not labeled "beta" it does support it and support will be able to find that documentation.
Keep in mind: This is a beta feature, and we do not recommend beta features for production environments, however, if your deployment requires the use of this feature, we recommend testing in a lab environment first.
Also, if this is a scenario to terminate a MPLS connection, we recommend using the MX in passthrough mode or terminate MPLS connections on the LAN side of the security appliance whenever possible.