Question about Visa

Hi there, 

I am a British Citizen and I am planning on being in Vietnam from 27th January 2018 - 10th February  2018. I understand there is a visa exemption of 15 days and I will be there for 15 days exactly but I wasn't sure whether I should apply for a visa on arrival just in case? Are you able to advise me on what I should do?

Thank you! 

 Kind regards,