If you see a consistent, stable 15ms greater than Openreach connected friends, there's probably not much to worry about because your response time to an on screen event is around 200ms at the absolute best.
Virgin Media connections always have a slightly higher ping than Openreach connections because the VM technology operates more slowly, so typically a VM connection has a minimum latency of around 19ms, compared to 15ms for Openreach. But that typical 4ms difference isn't going to improve your gaming, sadly. VM connections also exhibit far more peak latency spikes than Openreach connections - usually not to materially affect gameplay, but take a look at the two charts in this vaguely related post, and judge for yourself.
When for example connected to Sweden server they got around 30-38, I 40+. Even when we played on UK servers, my is around 20. While one of friends 10 other 15.
Dunno if they have Openreach, but speed for sure they have less. I know that speed not doing a lot of difference in ping, and also I know that Virgin always making a lot of steps to reach server when other providers less steps to reach server.
In this case looks like is better to switch provider, if I want to play games with less ping and more stable connection
Well, despite that fact that VM are on thin ice with me, I wouldn't recommend you switch ISP purely for the lower ping - the difference really isn't going to help you much. As per the linked post, if choosing an ISP and gaming were your only concern, then VM isn't perhaps ideal given that it is trying to push high download speed, content bundles, and pricing above more than a few Openreach competitors, but a reason to move on its own? Probably not worth the hassle, in my view.
If you have an unstable connection, you're unhappy with the price, or other issue, those could be reason to move, of course. And if thinking of leaving, make sure you're not in a lock-in period of contract because VM charge rip off early exit fees.
But you want to be depressed, and see how little difference a handful of milliseconds will make? Try this. And remember, no cheating, no gun jumping, no anticipation.