In bridge, are there different implications of overcalling 1NT in different positions?
Learn to evaluate this hand as being worth only 14 points, 14.5 at the very, very, most, and your bridge results will improve. 


No 10's, no 9's, no 8's, not even any 7's. The opponents will kill you with these cards leading through any and all quacks held by you and your partner. Then they will lead these cards through your kings to kill those too. Minus 1 point.
Minus one point for 4333 distribution. Goren was the world's best bridge teacher for three decades for good reason. Read his books, and recognize that in Chapter one he always stated that the 3-2-1 distribution points are not ruffing values, but indicative of general hand strength from the shape.


Open aggressively in third seat, for the preemptive value against a strong hand in fourth seat. Open this hand 1S in 3rd seat, and teach partner the Drury convention in that situation.

Open passively in fourth seat, so still  open this hand 1S and again teach partner the Drury convention for this situation.

I don't care that you are playing five card majors. 

Open 1spade anyways, and teach partner the Drury convention in this situation. Presumably you are asking here to learn better bridge. Learn to open strong 4-card spade suites in 3rd and 4th seat. This is part of becoming a better bridge player.

Don't open 14 point hands 1NT when playing 15-17HCP as your 1NT range.