Just a few more details:
- Go to Settings>System>About: Does it say U (= dual-core) or Q or K (= quad-core) in the CPU details?
- What is the Build version of your Windows 10 OS? (Scroll down a few lines).
Your minimum and maximum processor states are the default values. Try this:
Set Minimum Processor State to 50 for both.
Set Maximum Processor State to 99 for both.
The critical value is the Minimum Processor State. Try increasing the value to as much as 80. If you gain no improvement, you can reset the values.
I have to say I'm a bit surprised that you can play Shadows of Mordor with this CPU/GPU setup at all, and my guess is that the Lenovo is struggling to keep up regardless of the processor state values. Do you experience this kind of lag with other games as well or is it just Shadows of Mordor?
The reason it seems to play better on battery is probably that the system throttles down across the board while on battery - to save power - and when it's plugged in all the background services and features are running on their default settings. There are a number of tweaks you can do with Windows 10, including disabling notifications and pop-up messages. And keep in mind that Windows 10 will download and install updates automatically unless you set specific hours when it shouldn't ('Active hours').