How can I fix my Galaxy Ace 3 Wifi speed?

[AC Question]

I have a Galaxy Ace 3 since September 2014. I often experience some problems with downloading speed when connected to wifi network. The download speed can't reach more than 15 kb/s. This happens in 80% of the attempts to download something. This is NOT caused by the internet speed (all other devices connected to the same network have good speed). Sometimes the speed is good (2-3 mb/s) but only sometimes.

 

[B. Diddy]

Welcome to Android Central! Does this only happen on your own wi-fi network, or public ones as well?