I'm having a similar issue on my Lumia 1520. When I unlock the phone, it will show a loading screen on the start screen with the full loading animation and everything. Black screen, says Loading, and shows the blue dots loading animation. Sometimes, this will take around 2 minutes to get to the start screen. When this is happening, I can hold the Back button down to multitask and the start screen is the only thing running.
When I do get to my start screen, the battery will be quite a bit lower than it should and when I check the Battery Saver, it shows Internet Explorer as having used a lot of the battery, even though I have it disabled when not in use. This has been happening more and more frequently. This was happening before the latest update. If anyone has any suggestions, I'd appreciate it.