I was wondering why my "slide to unlock" was being extremely laggy today. Sometimes it had a lag of over two seconds, four at most. All the "slide to ___" were being laggy, and I was getting worried since I know it isn't normal. Turns out that all you have to do is power off your iPhone and turn it back on again. It was probably because I haven't shut my iPhone off in days
So if your slide is being laggy, shut it off 