There's a software update recently for the J7 2015 which is around 250mb. when it comes to slow charging, the question is, are you using the phone while being charged? if yes, then charging time will definitely be affected. also, using usb cables longer than what came with the charger could also affect charging times.
My J7 is fully charged for more or less two hours using the cable it came with, but took around three hours when I used a cable 1.8 meters long. the cable it came with I think is around 0.75 meters long.
