Yup, Sonicwall BWM is basically QoS, I imagine it would help solve your problem. I'm guessing your bottleneck is your WAN connection, although if it's your LAN connection you can do roughly the same thing on that. If you're overloading your Sonicwall's max connections or throughput bandwidth, this will not help you as much. You should checkt to see what security services you have enabled, as that will lower your throughput - on the TZ205 if you have IPS turned on you drop down to 60Mbps, and if you turn on Gateway Antivirus it's 50Mbps.
You'll need to set the max bandwidth available on your WAN connections, then set up BWM rules to prioritize your streaming traffic and/or guarantee it a minimum amount of bandwidth, then create access rules (or use existing ones) and attach the BWM rules to those access rules. It'll give you statistics to show how it's working. It's also easy to disable, if you run into any unexpected difficulties. Take a look here: https://support.sonicwall.com/kb/sw11092