Oh! of course. The perception that stories languish on the "new" page inspite of having received upvotes (not mine) was a qualitative observation rather than a quantitative one. May be the compete pool itself has grown larger and it needs more votes to get promoted.

What I am talking about here is that even after I have upvoted a story and refreshed the page after 15 minutes it still does not show the upvote.

Question of voting ring does not arise, the very thought is quite preposterous ! :) Unless it has a tendency to trigger false positives. If there was indeed such a tendency, I think that would have come to light sooner.

The first issue for you to consider is the continuous system load caused by immediately counting every single vote and/or flag on submissions. It makes a lot of sense to batch the tallying operations and only update every "N" minutes to reduce load. Additionally, since an up-vote on a submission will mark it so it's stored in your "saved stories" list, the overhead of immediate processing is most likely larger than most imagine. Also, there's the overhead and delays of multiple types of caching being employed. As always, it's a huge balancing act.

The second issue is how ring-voting, ring-flagging, and even ring-rating are constantly occurring since combating the problem is exceedingly difficult, and the rewards for successful abusive manipulation can be substantial. Abusive manipulation from multiple people/accounts is even more difficult to solve on any system designed to produce collaborative curation. Generally speaking, HN is collaborative curation, but attempts are made to prevent abusive manipulation.