I understand that you are getting fluctuating speed through your wireless.
Fluctuating speed is usually related to interference or security/monitoring software on the system, in some cases it can also mean a faulty hardware.
In the case of interference you would see the same behavior on the other laptop if you switch places, you may still test changing some settings on the laptop, specifically the power management of the laptop (in control panel), set everything to maximum performance. Also just for a test move the laptop sideways (since the antennas are located in different areas on a laptop you may get better speeds if the laptop is in a different position) this part is also easily tested if you have the change to move around with the laptop.
For security/monitoring software you would need to check your laptop for any kind of anti-malware or monitoring software installed. Try also disabling the firewalls and anti-virus software, you would be able to know if this is a software related issue if you boot into Safe Mode with Networking and test the speed there. This would help you narrow down what the cause to this issue is. Now if you get the same speeds in safe mode then it would be related to a failing network adapter.
It is also recommended to check the router firmware.
See the link below for some additional information/help: