We're about to start testing a change on the Oceania LoL server where surrender attempts between 15 and 20 minutes will follow the same rules as those after twenty minutes. We've been looking at the impact of early unanimous surrender now that it's been out for quite a while. From what we've seen games that fail a surrender 4-1 between 15 and 20 very often end up with a surrender or defeat around 20 minutes instead. That means the unanimous requirement is mainly just dragging out games. The original intent behind the unanimous requirement was to avoid surrender votes going through when a comeback's still likely, that's not happening very often though.
If this test goes well it's a change we'll roll out to all the other regions as well after a couple of patches. If it ends up creating unforeseen problems we'll pull it off Oceania once that becomes clear.
Finally as a side note, some of you might recall that we also used Oceania to test the prior surrender changes that introduced the 15 minutes surrender rules about a year ago. We're going with Oceania again this time because previous results were quite representative of most other LoL regions, so it's a proven test location for these types of changes.
Update: Turns out the patch that would be making this change isn't working as hoped right now. Looking into why that is and will update once it's enabled. For now surrender behavior should be just as normal.