Sind die Zinsen geringer bei einer Kreditkarte im Vergleich zum Dispokredit eines Girokontos?

This cannot be answered in a lump sum, as it depends on the terms of the bank and the credit card billing model.

In some credit cards, no interest is charged at all, because the total open amount is automatically debited monthly from the current account, other cards offer a choice between full payment and partial payment, with very high interest often being required for partial payment.