Performance differences between similar PC's

Hello. I have two PC’s.

First PC (I am making game on this one)

GeForce GTX 970 4GB

16 GB RAM

Intel i5 4690 x4 3.5 GHz

I am getting something around 90 FPS in my huge open world game (Packaged version for “Shipping”) on this PC.

Another PC is:

GeForce GT1030 2GB

8 GB RAM

Intel Pentium G5400 /3.7GHz, 4MB

On this PC I am getting only about 24 FPS (Packaged version for “Shipping” again)

When I am looking into performence, it seems like graphics card is in 60% of usage on the first PC, and 97-99% on the second one. But I have no idea why the difference in performence is that large. I will be very grateful for any advices or general idea what can I improve, or when should I look for. Thank you!