Unfortunately I am not able to view your video at this time, however from your description it sounds like a resource thing. Too many things using your memory. This could be cache build up, or items being displayed, or apps open. The simplest thing to do first is to restart the phone. Most apps dump caches at power down or on startup and this could be just what you need to pep up your phone. I wouldn't use the restart option I would simply power it down and give it a few moments to completely power down, and then start back up. If you try this and it works then you begin to notice over time that it is still occurring you may want to try a manual cache clean. There are apps for this and while some may be good or at least OK you can do this your self and it won't take long, and you won't get any ads or other junk some of these apps bring. Go to Settings>Apps>All and begin scrolling down the list stopping at your email app, Facebook, your SMS app, Hangouts, any other app that jumps out at you as one you think may be holding on to it's cache. Those for sure others if the mood strikes you. Do the cache clear option for each of them, and then restart the phone same as before. If this works for you and you begin to notice it creeping back more drastic measures should be taken beginning with the SMS app. We all get a hundred texts a day and probably only delete three. Over time, more with the stock messaging apps, i.e. Hangouts, and Messages, a build up of messages can slow down your device, causing the lag you've noticed typing and a lag in messages being sent. It likely affects other apps maybe not as noticeably. Backing up messages that you want to keep and deleting them from the app, especially MMS messages, will free up a lot of the memory being used to display them and make them quickly available. Also if you are using the stock apps for Messaging and find that this works to reduce the lag, you may want to consider a third party app. Most handle caches better than the stock app and may also handle the display side better. Just food for thought, if this turns out to be something that works or applies to you.