The issue of heating is very common these days but it is completely dependent on the type of usage.this is common across most of phones and the reason for that is either the material used for exterior of the device or the chipset that powers the phone.In case of j7 it is because of the build quality that it is heating.The interface and ui of the j7 prime is slowing down the phone.And also the charging of the j7 prime is very slow