I actually had the same exact problem you did--my phone was freezing and then restarting. I sent in my LG G4 on the 14th. I called LG and the lady on the phone emailed me the free Fedex shipping paper. It arrived at the LG facility in Texas on the 20th and now I am waiting for the return. I called LG today and they told me that it probably wouldn't ship until the end of this week, so the whole process will probably be around 2.5 - 3 weeks. I also have Sprint and was able to have one of the repair shops lend me a crappy phone since I have no other Sprint phone and know no one that has one. Unfortunately, they end up charging something like $75 to get the phone replaced through them which is either an overnight or given to you right there. It may be worth looking into if you need your phone immediately and don't have a replacement phone.
It really sucks and makes me wish that I had insurance or that LG had customer service like Apple. They wouldn't even send me a refurbished phone at the same time that I was returning mine. You would think they could just charge me for a phone and refund me once they receive my phone and inspect it. Some people say that it's what you deserve for not getting insurance. They're the same people that don't realize why Apple is so successful, because they go above and beyond for their customers.
It really sucks and makes me wish that I had insurance or that LG had customer service like Apple. They wouldn't even send me a refurbished phone at the same time that I was returning mine. You would think they could just charge me for a phone and refund me once they receive my phone and inspect it. Some people say that it's what you deserve for not getting insurance. They're the same people that don't realize why Apple is so successful, because they go above and beyond for their customers.