We would like to say that setting connection interval of 4 seconds is not a good idea in your case. Because in your case the peripheral has the information about touch sensor whether it is touched or not. Since peripheral peripheral does not initiate data transaction, it has to wait for the next connection interval to send the actual notification data to the central device.
Since your application involves BLE data transfer with very low power consumption and preferably fast connection interval, please go through following application note. It tells you about how BLE low power APIS are used to get lowest power consumption with reasonably small connection interval.
You can also go through the code example present in the same link.
Thanks and regards