You can split the counts into two different variables and then display them as a stacked bar chart.
| eval red=Case(count<15,count,count>=15,0)
| eval green=Case(count>=15,count,count<15,0)
| table job_id, red, green
your data will look similar to this
Case| Count| Red| Green|
1 8 8 0
2 1 1 0
3 11 11 0
4 55 0 55
5 44 0 44
6 233 0 233
7 48 0 48
8 10 10 0
Then create a bar chart with both Red and Green and use the charting.fieldColors setting in the XML to designate the colors of each variable
<option name="charting.fieldColors">{"Red":0xFF0000,"Green":0x00FF00}</option>
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