But 15-minutes cities aren't about traffic restrictions. I might be wrong but this seems like people are conflating low traffic zones (which can involve the kind of automated system to limit traffic that you seem to refer to) with 15 minutes cities, which is an idea in urban planning to decentralize services (the "15 minutes" is intended as "you can reach anything you need every day with 15 minutes of walk", not "you won't be allowed to travel more than 15 minutes")
If you have valid criticisms of the traffic filter trial in Oxford then that's fair enough, although I imagine Oxonians won't be particularly interested in hearing it unless you're a local resident.
It has absolutely nothing to do with traffic filtering or traffic restrictions, and this is simply misinformation (sadly, misinformation perpetuated by the political party with a majority in the United Kingdom). Nobody is going to be confined to a distance-based-radius of their home, and anyone stupid enough to believe this is a damning indictment of the UK's education system.
There are very valid criticisms of the "15 minute city" including the widespread surveillance required to enforce certain proposed traffic restrictions (by personally identifying drivers and only allowing access to some areas at certain times). Councils and national governments in the UK have long abused data gathering to the detriment of its citizens. Unfortunately the Guardian and its ilk have derided critics of these plans as far right extremists and conspiracy theories.