Hahaha, get 15's out of you mind. A stock tuned MT Sedan getting under 16.00 would take an amazing amount of skill if it's even possible.
After each run, you'll get a time slip. Don't worry about RT, reaction time. Unless you plan to compete soon, you don't need to even worry about trying to launch as the green light hits.
You want to focus on ET, elapsed time from when you began motion to when you cross the qtr mile line. And most importantly, your ET will mostly be affected by you 60' time, how long it takes from launch to 60 feet.
If you really want detailed advise, go the the start of this thread and read EVERYTHING. Otherwise, just try revving up to different RPMs on each launch until you find your sweet spot that nets you your best 60'...... then focus on shifting at ~5.5k.
Expert hint: You should still be in third when you cross the traps (finish line)