Clearing and reloading a list increases the structural changes within a model and will increase the likelihood of a of model save, thus increasing the import time. It also removes pre-allocated memory block designed to increase efficiency. Use a unique key to update to values rather than delete and re-load. Also consider adding a TRUE field to the data source which will allow you to know which records have been imported
Best Practices articles
Data Hubs Purpose and Peak Performance
Pre-Allocation in Lists and Impacts to Model Performance
Questions on this topic? See 1.05-10 Never delete list and reload the list as a daily occurrence in our Planual forum.