I own a LG-D855 which I bought refurbished running the bundled modified version of Android that LG provide.
After a few weeks I installed Cyanogenmod 12.1 and since then I've been updating weekly.
When I turn the phone on for the first time it runs very quickly. However after using the phone with a handful of apps for 15 or 30 minutes the whole phone slows down to a crawl.
I've installed an app which stops as many background processes as it can. After running this the phone speeds up again, but soon returns to it's previous state.
I bought an LG G3 as it rated very highly on lists of the best Android phones to buy.
Why am I having these problems? Are these common issues with the LG G3? What can I do to allow my phone to run more quickly?