Overheating can be anything from 'it feels hot' up to 'you can cook an egg on it'. Z5 does have an overheating problem when screen is on with full brightness or when using apps. But if you feel it is not the normal overheating, then one of your apps is running in the background and misbehaving with CPU. Especially if you also experience lagging and fast drain of your battery. I had this issue with Gmail app when configured to access a specific external Exchange account which kept the connection always on. If you can't suspect an app (a recent install, a specific pattern that this happens, etc) then a task manager app might help (such as Advanced Task Killer, Advanced Task Manager, ES Task manager, Smart Task Manager or SystemPanel 2). For your charging issue check if you are using a normal charger or a QickCharge 2.0 compatible. Obviously normal chargers will delay with this phone.
