Hi there, sorry for the delay, you appear to have posted two duplicate questions so there was confusion on which one to reply.
It is very unlikely that an employer can justify dismissal after 15 years of service just because you have received a caution. First of all this is not a formal conviction so is not that serious.
Even if it was a conviction, the employer can only consider dismissal if it has a serious impact on their ability to perform their job. So for example, a teacher convicted of sexual offences against children, a bank worker convicted of fraud, etc. Even then it has to be a serious effect it has on their job.
If you have performed your job for 15 years with no issues and suddenly you get a caution, then there should be no reason for the employer to dismiss you and if they do the dismissal is likely to be unfair and can be challenged.
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