I doubt it
First of all, if you used an initial running count of -20 with the KO count, the ending count should be +4, not -14. Therefore the average ending count of +2.5 that you observed with the 16 decks you counted is not unreasonable.
If you have observed some extremes in counts or session losses, this is not unusual when playing blackjack. I believe is it too risky for a casino to short cards in a shoe to gain more of an advantage over players.