Can i (Us/German dual Citizen) Cash out etfs in the us to cheapen the heavy capital gains tax?

I just got started on ETF's and was wondering how to cash out in 10-15 Years and i was thinking if it would be Possible to Cash out in the US (I have both Citizenships) on lower taxes. In Germsny Capital Gains tax comes out to about 30.5%, and i read in the US it is way lower if you hold it lower (I think only about 15,20% for that long duration). Is there a way to get a very short Residency, cash out, and come back to Germany? My Broker has both tax numbers, so i dont get double taxed.