AirPort Time Capsule number of users

In theory, yes. However, things tend to get mighty slow on just one AirPort router when there are just 12-15 active devices on the Wi-Fi network, so things are likely not going to work as well as the theory suggests.

Hopefully, you are not thinking about a business or commercial application here.

You will improve your odds of stable connections if you add another AirPort Extreme (or AirPort Time Capsule) and connect approximately half of the Wi-Fi devices to one AirPort and the other half to the other AirPort.

The two AirPorts cannot be located close together. Ideally, the AirPorts would be located a few rooms away from each other so that about half of your WiFi devices will connect to one AirPort and the other half of the WiFi devices will connect to the other AirPort.

In addition, sign up for the fastest Internet connection that your provider offers, if you have not already done so.

Connect the two Airport Extremes together using a permanent wired Ethernet cable connection. Avoid connecting the second AirPort to the first using only wireless, since this will always result in a loss of at least half of the available bandwidth on the network. In other words, you will have more wireless coverage, but you will have a significantly slower network.

There is no bandwidth or speed loss when the AirPorts connect together using a permanent wired Ethernet cable connection, so it is easy to understand why you would always want to use this type of connection when performance is important.