That employee has given 15 years of his services, its natural to witness change in bis behaviour with course of time. Termination will not solve the purpose, as there will be no guarantee that the person who will replace this employee, will be far better. I feel, management must discuss openly about his behaviour, and let him know, how his behaviour is unhealthy for the organisation. Make him realise about his mistake. Atleast a chance should be given for improvement.