I think breathing down their neck it's the worst thing you can do esecially when those 15 working days aren't over yet . If I as were to choose between e-mailing and giving a call I would have chosen to give a phone call , talk nicely , explaining why I called before the deadline .
To be honest assaulting them with e-mails and phones even if those 15 days are over it's not a smart move either since they are already stressed with not meeting the deadline due to heavy workload ..
Although there is no any other ANSP who has the same standards and policy and everything you ever dreamed of of an employer , and although I love UK and everything about its people and culture , and although I am dying to find out the outcome of my application ... I wouldn't call for anything in this world .