15 years is plenty of time to switch away from them. IPv6 is just one reason. It's a shit ISP. I ditched them as soon as I could and cited IPv6 as a reason, in case it made a difference (I also questioned my new ISP before I joined).

Virgin Media exist for two reasons: first they were given a monopoly by their Tory chums (Thatcher) and, second, all ISPs are allowed to make you sign absurdly long, anti-competitive contracts (18 months is common). If ISPs were treated the same as utility suppliers we'd probably be in a better place.