Trouble connecting to 4G when Wifi enabled, but low signal I have a Samsung S5 Neo (SM-G903F), Android 5.1.1

My I access internet apps/sites when i am close to my router, works great. But when I go up a floor, and am basically out of range from the Wifi router, the phone does not switch to 4G... but still tried to access Wifi, but evidently its not strong enough to actually connect - so I basically get no connection. I have to manually disabled Wifi, and then it connects fine. 

Is there a way to "lower the sensitivity" level, to allow the phone to connect to 4G when the Wifi signal is weak?

Thanks!
On Android 4.4, there is an option "Avoid poor connections" under Settings->Wi-Fi->Advanced(perhaps under the menu). You want to set this option on. 

This option is not present in Android 6. I'm not sure whether it's present in Android 5.1.