If the system is more than a year old, it may simply need a good internal cleaning and replacement of the thermal pads/compound that interface the heatsinks to the CPU and GPU.

@ejn63​  

isn't there any other solution?  

like customizing the temperature and speed?

What model G series is this -- G15 5530, 5560, etc.?

@ejn63​ 

its g15 5520

That makes it about three years old -- and if it hasn't been internally cleaned, that's still the very first thing to do.