It is usually recommended to have a refresh rate of around 20 ms when there is an active touch.
If there is no active touch for x duration, you can scan every 100 to 200 ms. You can switch back to active mode when there is a touch detected.
You can implement low power modes also in the in between time if the CPU is idle.
Refer to the code example
It is not required to poll the CapSense device from the master after every scan to know CapSense touch status. It is enough to read the slave device only if there is a change in touch status. To do this, you can have a host interrupt pin that is triggered by the slave device whenever there is change in the capsense touch status. The master has to read the slave device only when the interrupt is triggered by the slave.