Welcome to the Dell Community @NotSoCool
First try updating:
Intel Dynamic Platform and Thermal Framework:
If that does not help then try disconnecting the "Main" battery and then playing the game on AC only.
It requires loosening three captive screws and removing eight screws.
Dell Inspiron 15-7572 (P61F001) Bottom Base Removal and Installation:
Your system comes with a 3-cell “SMART” lithium-ion battery.
It communicates with the system using the "SMbus" to charge and discharge the battery.
If your battery is even at 90% it will constantly be requesting the CPU to charge the battery.
Which will slow the system down.
When the AC is not plugged in it does not send those same requests to the CPU.
That's why I asked for you to just "Disconnect" the battery and try running on the AC.
You do not need to replace all the screws until after testing.
Make sure In the Power Options under Select a power plan, choose High Performance.
Thanks for posting and for sending your service tag information. Apologies that your system is not performing as expected.
Your post doesn't indicate if you've been able to perform a systems diagnostics yet. Please run Dell SupportAssist or press F12 at startup, make a note of any error messages found and post back.
Here is information from the Dell knowledge base you may find helpful: How to Troubleshoot Slow Performance Issues
Let us know if that resolves your issue. Thanks.