I hope that I ahven't misunderstood your question but here is an articl that describes how MArkeot uses the SFDC API:
https://community.marketo.com/MarketoArticle?id=kA050000000Kyr6CAC
By default the sync interval is set to 5 minutes. This could be brought out to 10 mins or 15 mins and that would substantially reduce the amount of API calls in a 24 hour period. If you need this you can log a support case.