Many things affect WIFI speed. See https://www.cnet.com/how-to/home-networking-explained-part-1-heres-the-url-for-you/ You may have one of your other devices slowing it down. I have an Archer C8 with 22 WIFI and 3 wired devices using Xfinity 200 Blast service and many times I get over 200 on the 5GHZ and in the 60-80 range on the 2.4GHz when in sight of the router. I do have an extender which affects (slows) the speed. I do not use any cloud backup as that takes a lot of bandwidth. Sometimes it slows down I think due to the ISP and due to channel usage by nearby routers. Try different channels and band width to see if it helps.

@Denver49 

 

With 2.4Ghz I tend to expect around the 40s range or higher if I am close. Getting 15 Mbps seems low compared to getting 200 Mbps. With the wireless settings, try changing the 2.4GHz width to 40 MHz and the channel to 11, keep trying other combinations to see if you get a improvement in speed.