Is it normal for my new iPhone 15 battery capacity to drop 2%?

Yes it's normal based on tech statics, but it shouldn't be base on my experience.

My iPhone 15 Pro Max dropped 1% after 1 month of use and 25 charge cycles. My 2 other friends has 100% health on their iPhone 15 Pro Max, even though their charge cycles are 26 and 30. And my past iPhone 13 Pro Max and 14 Pro Max had 100% battery health for at least 11 months. So again I will say it's not normal.

Yes. Expect a 1 - 2% drop every 1 - 2 months.