The ping is measured in-game.

So does that include the "forward messages every 50 ms" delay?

Hmm, I don't know the traceroute, I don't live in there. How would it help?

Because the actual path taken by the packets may be different than the seemingly closest route.
Also, traceroute shows you where along the way the time is being spent, which would help you figure out what it is you need to address.
Trying to "fix things" without having good measurements of the current impact of what you're fixing and the expected improvement leads to wasted effort.

How much ping can that jitter add up? The CPU is staying up to ~15% all the time now.

The CPU utilization reported by a "guest" inside a virtualized environment doesn't tell you anything about what the "host" does to you.

Do you mean I should somehow optimise my game to let players play with a bigger ping?

Yes. A good rule of thumb is that a game needs to keep working up to at least 500 ms ping, and feel good at least up to 200 ms ping.