I think you'll probably find your dealership will only update your software if your car has a fault which requires an update to fix it, unless you want to pay to have it updated. They only get payment from MG if the update is necessary for whatever reason, so most are reluctant to spend what can be quite a few hours on updates, if they don't get reimbursed.
My SE LR is running R13, which I believe is pretty ancient, but I don't have any real problems with it, so I figure if it ain't broke, why try to fix it?