UFO Sighting in Mustang, Oklahoma on July 4th 2015 – Thought it was the ISS, until it changed 180 degree direction and was moving way too fast

My family and I were in the backyard observing the July 4th fireworks display. While I was looking up I noticed a "star" moving quite quickly in the sky in a SE direction. I observed it for about 10 seconds to acknowledge if it was just a plane flying high overhead, but the object was solid white (looked like the planet Venus, only it was moving). It was hard to tell exactly how high it was but I would guess a good 3-5 miles high. I then came to the assumption it was probably the International Space Station flying overhead as I have seen it fly by plenty of times. I motioned for my family members to check it out and in the 5 seconds I took my eyes off the object it had completely changed direction 180 degrees and proceeded to take a straight NW path. The speed had to be incredible because it went from being straight overhead to zipping off into the horizon in about 15 seconds.