Highlight consecutive 15 data points within positive and negative range

Hello All,

I am working on a process control chart. i want to highligth the data points between two range (+ve and -ve)

If there are continious 15 or more points within the range then they should be highlighted. 

I am having data points based on date.

example-

date      point  (upperlimit)    (lowerlimit)

15 jan     10          15                    -15

16 jan      12         15                    -15

and so on. 

I have also attached an image for reference.