Turns out I cannot close my own question as duplicate, because the other question I found is not on this site but on meta.stackexchange.com.
Keeping the question to allow others to find this answer that I found here:
What happens with votes cast with rep < 15 exactly?
What does recorded mean exactly?
Recorded in database, separate table. (Not along with ordinary votes)
It can be queried via SEDE, as explained in this other answer I
Can the owner of the up-voted question/answer see in any kind, that he/she got my up-vote?
No, this is not possible.
Does he/she get rep for this?
No, no reputation is gained to any side.
What happens with these votes, if I reach the 15 rep? Will they take effect subsequently?
As explained in the answers to this other
nothing happens to those votes, and they don't have subsequent effect,
you'll have to vote again.
Or are they just recorded for my "vote-history"?
No, they are not part of the votes tab in the profile.