Dear Yuqi Chew,
1) I would advise you to read the information regardign the DoSV on our website (
https://www.uni-hamburg.de/campuscenter ... heide.html) as well as the DoSV FAQ (
https://www.uni-hamburg.de/campuscenter ... -dosv.html).
2) "Since the places according ZZVO is 15, the eliminated applications need to be at least 27 for me to be admitted. Is my understanding correct?"
I am not sure what exactly you mean by "eliminated".
The first 15 applicants in the ranking have received an admission offer ("Zulassungsangebot") or admission ("Zulassung"), depending on the specific constellation of their applications. If an admitted applicant does not accept the admission by submitting the application for enrollment within the enrollment deadline, or if the application for enrollment is not successful, the next applicant in the ranking receives an admission offer or an admission. Furthermore, since it is possible in the DoSV to apply for multiple degree programs at multiple universities applicants can be removed from the ranking at any time, if they receive an admission or an admission offer by a different university or for a different degree program.
3) "I have read that the historical cut-off rankings for B.Sc. Informatik is around 2.5"
This is not the relevant information for you.
You read the information regarding the EU quota, which has different selection criteria than the non-EU quota (see
https://www.uni-hamburg.de/bonuspunkte).
The list with the information regarding application procedures of the past years for the non-EU-quota are available in the following document:
https://www.uni-hamburg.de/campuscenter ... cht-eu.pdf.
Best wishes
Thomas Walter