Can some one help me to figure out why the last 15 min period doesn't show up on chart?
As you can see in the chart setting I listed the RTH from 6:30 to 13:15:00 (13:14:59 didn't help either).

Not sure what the problem is, the "N" period represents the last 15min

tr8er 

Not sure what the problem is, the "N" period represents the last 15min

Isn't it supposed to print "o" period after N since it ends at 13:00 with 30 min for each periods?

The letter "N" is the period from 13:00 to 13:15.

The day-session you want to see lasts 6 hours and 45 minutes, so this means if you are using 30min-candles, you should see 14 candles and your chart shows 14 candles, the letter "O" on the far right side is a bit curious, no idea why this is, as I see it this ticks should still be part of the "N" session, I don't use sierra-charts, but I would UNCHECK "use evening session"