Hello Andrew,
Welcome to Microsoft Community.
According to your description, your Surface Studio 2+ will stop recognizing your Surface Pen after a fixed 15 minutes? So at this point, do some tests:
- If using finger instead of the Surface Pen, can you touch and draw on the screen?
- If the problem can be resolved after restarting the computer, can I understand that clicking on the Start menu - Account - Log out will achieve the same effect?
- If only the screen doesn't recognize the Surface Pen again, will you be able to see the Surface Pen in your device after clicking on the Start menu -- Settings -- Bluetooth & Other Devices? This is to confirm if the problem is simply that the screen is no longer receiving the Surface Pen's signal, or if the Surface is no longer able to recognize your Surface Pen via Bluetooth.
I believe that you've already installed all the firmware updates, so you must have downloaded the driver and firmware package for Surface Studio 2+ from here, and then manually installed it:
Download Surface Studio 2+ Drivers and Firmware from Official Microsoft Download Center****
If the problem persists, I recommend that you try to do a complete diagnosis of your Surface with the Surface Diagnostic ToolKit, and make sure you receive some diagnostic suggestions at the end:
Fix common Surface problems using the Surface app and Surface Diagnostic Toolkit - Microsoft Support
If you have any additional information, you can let me know together with the test results.
Best Regards,
Mitchell | Microsoft Community Support Specialist