It can’t be transferred into the defined benefit Royal Mail Pension Plan because that closed to new entrants in 2008 and is due to close to everyone else in 2018.
Everyone starting from 1st April 2008 is eligible to join the RM Defined Contribution Plan and a transfer into that is a possibility on paper. Plan guide here: https://www.zurich.co.uk/internet/works ... 714073.pdf
I’m no expert on the NHS pension, however I think the answer to your question lies with your NHS pension rules!
A simple Google search throws up this document: https://www.nhsbsa.nhs.uk/sites/default ... 5.2017.pdf
Where it states: you can transfer to a registered personal pension plan, including a stakeholder pension arrangement (only if you have less than two years qualifying membership).
With 14 years in the NHS, that seems to rule that idea out. So basically no you can’t transfer.