Laptop Description: 
I own an EVGA SC15 Gaming laptop (less than a year old) with the following specs:
CPU: Intel i7- 7700HQ @ 2.8 GHz- 2.81 GHz
GPU: NVIDIA GeForce GTX 1060, Core: 1455 MHz, Memory: 8008 MHz, GDDR5, 381.99
RAM: 16384 MB, DDR4, 1300 MHz, Dual-Channel, 16-16-16-39
Storage: Toshiba NVMe THNSN5256GPU7, 256 GB. Secondary: 1 TB Seagate ST1000LM048 HDD
AntiVirus: BitDefender Total Security. (If it is of concern)

Since around a month ago, my CPU has been reaching temperatures above 90°C with just 15 mins of gaming while plugged in and drops back to around 60-70°C within a minute after I quit playing. I never had this issue before.
I haven't noticed this earlier, but 'now' my CPU runs at a clock rate of 3.4 - 3.7 GHz when plugged in (even when idle). Earlier the CPU would run at such speeds only when multitasking or when on load. I haven't attempted to overclock the CPU or GPU although my laptop allows this out of the box.

I have tried blowing out the dust, updating the BIOS, checking for viruses, adjusting the fan control. I assume the thermal paste wore off(It has been less than 1 year since purchase). But the clock speed seems to be the main problem.

Below mentioned are the temperature and clock speed readings at idle, while gaming and after gaming:
(Note: Ambient temps are around 37°-40°C around here)

Idle (on battery) -- Clock(CPU) : 798 MHZ , temp : ~45°-50°C 
Clock(GPU) : 139 MHz , temp : ~45°-50°C
Idle (plugged in) -- Clock(CPU) : ~3490 - 3791 MHZ , temp : ~48°-55°C 
Clock(GPU) : 139 MHz , temp : ~45°-50°C
Gaming (15mins, plugged in) -- Clock(CPU) : ~3490 - 3791 MHZ, temp: ~85°-90°C
Clock(GPU) : 1809 MHz , temp : ~83°-85°C
2 secs after quittting -- Clock(CPU) : ~3490 - 3791 MHZ, temp: ~80°-85°C 
Clock(GPU) : ~1800 MHz , temp : ~80°-83°C
1 min after quitting -- Clock(CPU) : ~3490 - 3791 MHZ, temp: ~65°-75°C 
Clock(GPU) : 139 MHz , temp : ~65°C
10 mins after quitting(on fan boost) -- Clock(CPU) : ~3490 - 3791 MHZ, temp: ~50°-55°C 
Clock(GPU) : 139 MHz , temp : ~55°C.

Sorry for the lengthy descriptions. Any insights and help would be appreciated!!

 
Is laptop on a hard surface ?
 
 
Has Windows updated your PC ?  What Version (1803 ?) & Built Number (17134.xxx ?)  are you On ?

Check your Power Options in Windows
 
Go To:

     "Control Panel\All Control Panel Items\Power Options"
 
     ---> Change Plan Options

     --> Change Advanced Power Settings

     --> Processor power management

Liquid metal TIM and a modded bios fan curve you probably can get temps down to low 80s C under gaming load.

ty_ger07

saccaed
Liquid metal TIM and a modded bios fan curve you probably can get temps down to low 80s C under gaming load.

Taking the motherboard out of the SC15 in order to replace the thermal paste is not easy.

If replacing the TIM at all is daunting, liquid metal will be even more so. However, if TIM replacement is to happen, may as well go with the best. That said, liquid metal will brick anything and everything if misapplied.

Cool GTX
 
Is laptop on a hard surface ?
 
 
Has Windows updated your PC ?  What Version (1803 ?) & Built Number (17134.xxx ?)  are you On ?

Check your Power Options in Windows
 
Go To:

    "Control Panel\All Control Panel Items\Power Options"
 
     ---> Change Plan Options

    --> Change Advanced Power Settings

    --> Processor power management

I lowered mine to 5%, and it does seem to run cooler.  Can you explain what this change actually does?