Why is my Galaxy S6 edge plus's battery draining so fast?

I recently bought this phone and I have noticed that the battery is draining fast. The battery level dropped by almost 10% in 15-20 mins while I was just doing normal texting. I have used the phone in safe mode as well and in standby mode the phone just lasted for 24 hrs as opposed to 3 days of standby time as claimed by Samsung. So I was just wondering if there is an issue with my battery or with the phone or if this is normal in S6 edge plus?

Stats according to GSAM Battery Monitor,
Used 85% in 20 hr 10 min
phone - 0%
Screen - 2 hr 47 mins - 25%
Phone radio - 20 hr - 6%
Wifi Active - 20 hr - 3%
Held awake - 7 hr - 1%
App usage - 64% (With Android OS - 24% and Kernel - 10%)

I have already tried restarting the device and the problem still exists and always keep location off. And in terms of data I keep my wifi on and the apps that I use r only 3-4 like facebook, whatsapp, instagram. The main source of battery drainage is android system and screen. I was wondering is it possible that there is a problem with my battery/hardware and I should get it replaced? or it just could be a bug in the system that can go away after the marshmallow update? Coz originally I thought that there is a problem with my battery but now it seems like it could be an Android OS bug.