A connection speed of 8 Mbit/s is about 1 Mbyte effective download speed for all of your devices. Usually the speed is asynchronous, so the upload speed should even be less. The more devices share that bandwidth, the less speed a single device is able to gather. You could try turning off all other devices for testing if there's just too much concurrency on your network, as modern devices tend to jabber all the times with the internet.
In my opinion, a wireless connection has one big drawback, that is quite a large latency. While streaming to your TV, a connection is already established and you can gain full speed of your internal network (different to your internet connection). The latency comes mainly into account while negotiating a connection to the internal network, as well as the internet. The time to establish a connection with a wireless network in general is much higher, than with a wired network. That's why I use a Gigabit Thunderbolt to Ethernet adapter on my 2015 MBP for a wired connection. Consider that modern operating systems like macOS Sierra or High Sierra produce much traffic for many different services all the time. Especially if you do a restart or wake up the Mac, then it's quacking a lot and that with a large delay due to Wi-Fi's nature. I just can recommend to use wired Ethernet instead of Wi-Fi, whenever possible.
Of course there are possibilities to speed up a wireless network including:
- assigning a fixed IP address to your Mac (outside the DHCP range of your router setup) or at least verify that your router can serve a dynamic IP address through DHCP correctly for all of your devices
- switch between automatic and manual Wi-Fi channel assignment, if you're on 2,4-GHz (there are just 15 channels) or try using the 5 GHz band (makes sense if there are a lot of wireless networks in your neighbourhood)
- check the router firmware and update to the latest version and check the router settings for the sending signal strength
- test the signal strength that your Mac receives and on demand amplify the signal with the help of repeaters or an additional access point
- sometimes a new router is much more capable in handling an increased amount of network traffic, compared to models that have come into age
As a starting point read about checking Wi-Fi issues at
https://support.apple.com/en-us/HT202663
