I've flown TK via IST to and from the US several times and never has the SSSS. There are more factors involved or they'd have maybe a couple thousand people a day with it considering how many flights TK has to the US.

I wouldn't worry about it, and if one of you gets it and the other doesn't then hand off all of your carry on items to the other before entering security. The screening goes amazingly fast if you have nothing to screen.