When our baby was born on 18.06 she weighed 3235gr in hospital. Now she weighs 3030gr after 15 days. Is it normal? How can we say nursing is fine?

A baby Dr! Your baby needs to be seen by a doctor. It will be good to have regular checkups during these next few years and forming a relationship will be very good. It'd good that you feel nursing is going well. Make an appointment or just walk in to a clinic as soon as possible. Best!
Watch carefully. Newborns normally lose weight in the first week. Do check her weight regularly and if her weight does not increase from the 3030 gr now, in a week, be sure to see her pediatrician.