Since you have a warranty, call Dell to see if they'll exchange the system board under warranty.  
Hello, I bought new laptop latitude 5520 a month ago, CPU I5 1145G7, and I noticed that the bios and the task manager show the wrong CPU speed 1.5 GHz instead of 2.6 GHz, I checked the official Intel website, and I found that the base speed is 2.6 GHz, even when deactivating the Speed Step feature in the bios nothing was changed. [IMAGE]  
Wrong CPU base speed 1.5 GHz instead of 2.6 GHz