As far as I know walang ganyan para sa "No Root". Dapat Rooted talaga yung phone mo. Pwede naman bumili ng router for limiting the speeds of connected devices.
Pero if per app basis yung tinutukoy mo sa speed limiting kailangan niya talaga root.
Pero if downloading lang yung kailangan mo ilimit yung speed then use "ADM - Advanced Download Manager". Nasa playstore, meron siyang speed limit per download pero kind of finicky yung limit niya kasi minsan sumusobra or kulang sa sinet na speed.