Performance issue on iPhone 5

Hi guys,
I’m getting some weird performance issues on iPhone 5 - the game lags when the user taps the screen to change direction. It doesn’t happen on iPhone 6/iPod 6g/iPhone 4. Tried to experiment with disabling sounds, changing fixed timestep, but nothing helps. Here’s my Update code which seems to be a problem:

	void Update ()
	{

		if (Input.GetButtonDown ("Fire1")) {
		 if(started)
			{
				gameController.IncScore ();
				if (nextLos == 0) 
				{
					index += ballDir;
					if (index == TrackPath.currentPath.angles.Length)
						index = 0;
					else if (index == -1)
						index = TrackPath.currentPath.angles.Length - 1;
					ballDir *= -1;
					dir = Quaternion.Euler (0, 0, 180) * dir;
				} 
				else 
				{

					index += ballDir;
					if (index == TrackPath.currentPath.angles.Length)
						index = 0;
					if (index == -1)
						index = TrackPath.currentPath.angles.Length - 1;

					   dir = Quaternion.Euler(0, 0, TrackPath.currentPath.angles[index] * ballDir) * dir;
					pathNo += ballDir;
					if (pathNo == -1)
						pathNo = TrackPath.currentPath.angles.Length - 1;
					else if (pathNo == TrackPath.currentPath.angles.Length)
						pathNo = 0;
				}
            
			}
			else {
				started=true;
				gameController.tapToStart.GetComponent<PopUpEffect> ().StartCoroutine ("SimplePopDown");
				if (nextLos == 0) {
					ballDir = -1;
					index = 1;
					dir = TrackPath.currentPath.startDir2;
				} else {
					ballDir = 1;
					dir = TrackPath.currentPath.startDir1;
				}			
			}
			if (pathNo == 2)
				tpJumpsCount++;
			else {
				keyCountdown--;
				if (keyCountdown == 0) {
					gameController.SpawnKey ();
					keyCountdown = keyDelay;
				}
			}
			nextLos = next2Los;
			next2Los = Random.Range (0, 4);
			if (v < 7f)
				v += .2f;
			player.velocity = dir*v;
		}
	}

void IncScore() is just score++; ScoreView.text=score+"";
What’s interesting, the longer the game is running, the smoother it gets - after couple minutes running it’s perfect. It also seems to run a little better on iPhone 5 with ios 9 - lags on tap are not that often - but still happens. On ihone 5 with ios 8 - the lag happens almost each time you hit a screen.

Can you see anything suspicious? Or you had similar problem with iPhone 5?

That was font issue - changing the font file to .otf version found in web helped.