Hi,

May I know who is your internet service provider? And what's the bandwidth  you paid?

Please connect your computer to the main deco and test the speed you can get from it.
Note: Please show us a screenshot of the speed test result.

Then in order to do comparison analysis, please connect your computer or smart phone to the 2nd deco and run the speed test and show us the screenshots.

Please check the link speed of your computer/smart phone as well.
Note: How to get the link speed: https://www.tp-link.com/en/support/faq/2265/

Below are some suggestions you can give it a shot as well.
1. Please set QoS as standard. Open Deco app, go to more-Qos.
2. Please clear all high priority. In QoS page you can see device priority, click high priority and then you can clear them.

3. Disable the antivirus function, all the 3 rules. 

After that, please run the speed test again and check whether it work.

Thanks a lot, and have a great day.

Jorma wrote

I just installed the Deco P7 system. I'm getting 850/100 to the main router, but it only gives 450/70 just close to it. When using another device in another room, I only get 4/10!!!