how is this going to cause a large account to think twice about self voting at 3 minutes
Someone looking to vote for profit (or bots doing the same) will vote at 3 minutes or 15 minutes or whatever is required. They will figure out it and play whatever games are required to maximize profits.
The idea of shortening the timer is to get it out of the way of new or casual users who aren't going to play these games. If you see something you like and it isn't heavily voted, you should just vote for it, not set a timer to come back 15 minutes later and vote for it. Nobody does that.
The timer is a game for bots, which does have some useful secondary benefits for the platform as a whole, so I don't mind having one. But let it run its course on "bot timescales" not get in the way on human timescales. (As noted in the post I think it should be even shorter, but 3 min is better than 15 min.)
I'm one of those that just vote pretty much when I see it sometimes i will wait a few minutes, I rarely see anything when it is fist out because I rarely look at the new tab. The only vote I don't like is the one I give on an old post 7 days old or more, have done that several times, and I do not understand how people can resteem things that are 2 months old, but glitches happen I guess. People voting for maximum profit are going to like you said, vote for maximum profit, and there really is nothing wrong with that.
3 minutes works, it is long enough to see if you want to vote or finish reading the post.