slow download in play store of xiomi mi redmi 3s miui 8.1.1

xiomi redmi 3s has some problem.when i download any file from play store over wifi which is larger in size than 50 mb then the peak speed of my internet gets slow approx. it gets 5 to 8mbps only but my actual speed is approx.20mbps and when file size is less than 50mb then it use full speed which is approx.20mbps. it can only happen in downloading form play store i did all the things but it would neve improved.

from Android Authority Forums http://ift.tt/2nDzZuw
via IFTTT