PowerBI Semantic model Refresh taking long time

there are could be numerous reasons, for example:
- it could be your Data gateway resources if you use one for refresh, 

- could be capacity/Power BI service busy with other task (you have compelx transformations in Power Query or load tones of data that need to be compressed)
Take a look at this article, using this aproach I track how much it takes to load and process data and identify slowest queries to optimize:
 Visualize Power BI Refresh using Semantic-link - Phil Seamark on DAX

Hi Ira_27 ,

Thank you for engaging with the Microsoft Fabric Community. Here are a few quick checks to help identify where time is being spent.

1.  Download the refresh history for the dataset and review how time is split between Data Load and Processing.
2. For Premium/PPU, use the Capacity Metrics app to check CPU, memory usage, and any throttling during the refresh period.

3. Make sure that intensive Power Query steps are folding to the source; if not, the Service handles more processing.

4. Large single partitions and columns with high cardinality or width can increase processing time. Partition large fact tables by date and remove unused columns.

5. Gateway (if used)Check CPU/memory and queued requests on the gateway. High activity can slow things down before source queries run.

For a quick improvement, enable Incremental Refresh to process only recent data instead of the entire history. This change often has the greatest impact on large models.
Helpful Reference: Incremental refresh for semantic models in Power BI - Power BI | Microsoft Learn

-Yugandhar.