Have you performed a network survey/scan to see if there are any other WiFi networks around you? You don't say what frequency your network is operating on, but if it's 2.4GHz then there are only three (sometimes fewer) channels that do not overlap.
If anyone else has a WiFi network close to the channel you are on, then sometimes their network will transmit on some of the same frequencies your network is using, causing interference. This results in the packets being resent, increasing latency and lowering overall bandwidth.
If their network is on the same channel as yours, then you will be constantly trampling on each others' traffic. A WiFi connection speed of 64Mbps is a little unusual (it's not a common speed), which suggests that there could be quite a bit of interference.
If you do a scan with a program (or phone app) that lists what channels each network is on then this might give you a hint about whether moving your network to another channel might improve your signal quality.
If you are able to move your whole WiFi network to 5GHz instead (and all devices you wish to connect work at 5GHz), then the larger number of available channels will give you much more breathing room.