The onboard Realtek RTL8723BS wireless adapter is an SDIO adapter; SDIO is slower than PCIe-based wireless adapters. Wi-Fi speeds can be very slow, depending on many factors:
If there are other Wi-Fi routers nearby. Router channel is set to Auto (and so is everyone else’s).
How close the unit is to the router (router is in another room; signal passes through walls/floors).
Interference from other devices (mobile phones, cordless phones, microwaves, Bluetooth devices, or baby monitors.
You can try the following:
Eliminate interference with nearby wireless devices (like microwave, cordless phones).
Experiment with setting the router channel to a specific one, not Auto. Note: 2.4GHz can use channels 1, 6, and 11.
Try hooking a second router or a router extender to your main router to spread the signal throughout the house.
Disable the onboard wireless in BIOS and use a USB-based Ethernet adapter. Wired Ethernet is always going to be faster than Wi-Fi.