Take a look at the Quality Information at this link.
MKL15Z128VFM4 Product Information|NXP
For the MTBF and other Reliability data request;
I would need to ask you to please open a private ticket requesting this information so NXP Quality team can provide you with the requested documentation.
You may see how to do this on the following community document:
https://community.nxp.com/docs/DOC-329745
Thanks,
Philip
