Questions on Stack Exchange scoring some number of downvotes are not getting into active feed. Guess there are reasons why it´s so, but the question is not about it. The problem is once your question got enough downvotes it becomes more or less invisible for the users, so even if the question gets improved it´s unlikely somebody will see the improvements. So since politics has a relative low threshold of -3 I am asking to increase it for example to -7 like on meta. I personaly think that -5 would be a good new threshold, since also 5 votes are necesary to close a question.
I'll start with the bad news: I'm afraid this simply isn't something that anyone on Politics.SE has the power to do. This is a network-wide setting, and not something that can be changed from site to site.
If you really want this to be implemented, you would have to go to Meta.SE and make the case for it there. However, I doubt this request would be well-received there, as most of your points are already covered by existing network features.
The problem is once your question got enough downvotes it becomes more or less invisible for the users
Not necessarily. I personally always use the "Recently Active Questions" tab specifically because it doesn't hide heavily-downvoted questions, and I'm sure I'm not the only one.
even if the question gets improved it´s unlikely somebody will see the improvements
Again, not necessarily. As well as checking "Recently Active Questions", if you want to keep an eye on a specific question and see if it gets improved, you can follow it and you'll receive notifications if it gets edited. Again, this is something I routinely do with posts I feel are low-quality and/or liable to cause controversy.
since politics has a relative[ly] low threshold of -3
As I said before, the threshold is a network-wide setting, not something that varies from site to site. The -3 threshold isn't "relatively low", it's the same as every other site on the network. It may seem low simply because Politics.SE is a magnet for highly-opinionated and/or controversial questions that end up accruing large numbers of downvotes.
TL;DR: We can't do this, and we probably wouldn't even if we could, because there are already methods available for users to check if a downvoted question has been edited.
There is no need to increase the amount of bad questions that can be seen on the activity page and a score of -3 seems acceptable for hiding questions on the main site.
The score is lower on meta because there is a difference in the way voting works and down voting is also a sign of disagreement with a post or the idea in the post.
I would wholeheartedly agree with Joe W on questions that don't have answers, but when there are answers, things are different. Especially if there are good answers, it's really a shame that these good answers are no longer visible together with the bad question. Ideally it would be good to consider whether the bad question has good answers and then define the question's visibility in terms of the bad question's ratio to good answers.