Count If Start Datetime and End Datetime is less than 30 seconds

I need help in getting a count if the difference between a start and end datetime range is less than 15 minutes.
Column A1:A100 contains the start datetime, e.g. 1/23/2017 12:26
Column B1:B100 contains the end datetime, e.g. 1/23/2017 13:26

Idea is countif B1:B100-A1:100 < 15 mins.

Sample data attached

Attach a sample workbook. Make sure there is just enough data to demonstrate your need. Include a BEFORE sheet and an AFTER sheet in the workbook if needed to show the process you're trying to complete or automate. Make sure your desired results are shown, mock them up manually if necessary.

Remember to desensitize the data.

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Thanks Shukla. Sample data attached in the original post.

g2=SUMPRODUCT(($C$2:$C$25>0)*($C$2:$C$25<=$B$2:$B$25+TIME(0,15,0))*($A$2:$A$25="Project"))
g3=SUMPRODUCT(($C$2:$C$25>0)*($C$2:$C$25<=$B$2:$B$25+TIME(0,15,0))*($A$2:$A$25="Research"))

Or Try

G2=SUM(1*(IF($A$2:$A$25="Project",(IF(ISBLANK($C$2:$C$25),10^10,$C$2:$C$25)-$B$2:$B$25)*60*60*24,"")<=900))
G3=SUM(1*(IF($A$2:$A$25="Research",(IF(ISBLANK($C$2:$C$25),10^10,$C$2:$C$25)-$B$2:$B$25)*60*60*24,"")<=900))

...confirmed by pressing CTRL+SHIFT+ENTER to activate the array, not just ENTER. You will know the array is active when you see curly braces { } appear around your formula. If you do not CTRL+SHIFT+ENTER you will get an error or a clearly incorrect answer.