AC1200 cable modem router model C6220

Firmware on the C6220?

How much distance are we talking about between router and each device?  House materials? How big is the house?

What are the devices specifically? roku/apple/etc. 

Streaming 1080p/4k?  

 If you're hardwired into the router, what speeds do you get? You say you pay for 150mbps but your speedtest gets less. Is this over wifi? 

This is a hard one as several things impact wifi streaming, not just the router.  It comes down to wifi interference, the device you're using, distance, concurent streaming, etc.

There's many differnt things you can attempt to try to optimize signal and throughput.  

1. Try doing a wireless scan and seeing if you're wifi channel is on the most optimum channel. You can change channels to try to keep yours on the least congested.

2. Place different streaming devices on different bands. If you're streaming 4k, 5ghz is going to be best as it has higher throughput than 2.4ghz. Problem is it doesn't travel as far.

3. Distance. Is your router centrally located or is it on one end of the house?  Try to place it as close the center as possible for best coverage.

4. Device specific. Streaming 4k takes a fairly solid/reliable connection. Not all streaming devices or older device have the best wifi antenna or chipset. If you have the option, a hardwired connection is best. Either ethernet or powerline can help with this.

5. Gaming. The most important thing for games is latency and upload speeds. Usually download is fine because providers will sell you a very fast download speed but limit your upload to much lower rates.   Upload gets overlooked a lot. With 4k gaming, upload is becoming even more important due to high resolutions. Plus latency is significant for gaming. For gaming, the optimum solution is a hardwired connectio. Either ethernet or powerline. Or having the gaming device directly connected and the streamer on wifi.

Your running a base level router in the C6220. Not saying its bad but it isn't a high powered router with super fast speeds. If you're house is large, your running high bandwidth device, or having lots of wifi interference, the C6220 might not be up to the task.  You can definitely optimize by making sure you're on the correct wifi channels, have the router optimally placed, maybe moving either the streaming device or gaming device to a hardwired connection (if they run fine if only one is active). Even with the best of gear, 4k/gaming can put a load on networks. I had to place all my 4k streaming devices either on ethernet or powerline because of wireless congestion in my area.  

So basically I'm saying, try doing a little optimizing to see if it helps. If it doesn't you can try connecting via ethernet or powerline to see if that helps. Let me know how this goes.