why is Teams so slow and unresponsive when with more then 10 people in the call

Let everybody knows if turning "Read Receipts" off actually helps.

If this helps (so at least we know the culprit) this does not mean its a good move, because now you won't be able to let others to see when you read their message, and also you won't see when they read your messages, which makes Teams another Email client where you have no idea what happened to your message and why they not reply.

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Can you tell me what hardware you have (i.e. is that descent computer) and also what Anti-Virus/Anti-Everything you have. I can tell you one thing for sure: if you have 45 different security Agents installed on your machine because your Corporate security guys are insane and all they know is how to protect perimeter (i.e. their mindset got stuck in 90s) you are definitely a victim of the Corporate Security who really does not care about your user experience and your productivity. I worked in large company before where Teams was so slow that to join meeting you need to start joining 15 minutes before meeting so hopefully you can join in time.

Another big thing is VPN. Are you on VPN? If yes - HERE YOU GO. Please read about VPN issues, and why it is EVIL for all cloud services including Teams and Microsoft 265 in general. I won't list all the issues here, you can search for Split VPN Tunnel for Teams and you can read yourself.

Hope this can help. Waiting for some news and updates from you!

The slowness is nuts! It's extremely inefficient for trying to communicate with my business associates while working remote. I will just type and nothing appears and then all of a sudden it appears & sends 1/2 of the message while I am still trying to typing it. A co-worker said turning off Read Receipts helps. I am trying that now.

Also definitely try new meeting experience as this is very cool and works great!

I'm curious how many people who reported this issue here are using VPN to connect to On-Prem. Reason why I ask is because this is a typical experience (slow, sluggish, hanging, etc.) when you access Teams (which is obviously Cloud Application) through your corporate Firewall / VPN / Proxy servers and this behavior is expected.

If you do use VPN and you have slowness issue with Teams but your organization allows you to connect to Teams without corporate VPN try closing VPN and test Teams again and report your experience. It is well known issue and the only fix for this is implementing Split Tunnel VPN (search Google for that and you will see).

Another issue (also well-known) is if you use any third-party Anti-Virus / Anti-Spyware / Anti-Malware / Whitelisting tools like McAfee, Carbon Black, FireEye or equivalent. Those are well-known to slow down your computer, and what is worse when you look in Task Manager you can see that Teams is causing high CPU utilization while in reality it is caused by constant scan by third-party tool.

To prove that try using your personal, non-corporate computer (even slow Surface 2 should work great) and you most likely will see how fast Teams is! Either you chat, create or edit documents or join online meeting with full HD video and audio it should be perfectly fine! I can tell you that Teams is very snappy application and there is nothing to fix!

Hope this can help to some people here. Please report back your results!

I switched to the "new meeting experience" and have much better performance now in nearly all conferences. https://techcommunity.microsoft.com/t5/microsoft-teams-blog/new-meeting-and-calling-experience-in-microsoft-teams/ba-p/1537581