The victim, with his arm in a cast, is seen to be dragged to the floor by his neck before his attacker says "I'll drown you" while forcing water from a bottle into the victim's mouth.
The incident is said to have taken place on playing fields at Almondbury Community School in Huddersfield on October 25.
Barry Sheerman, MP for the town, said he had been supporting the boy and his family.
He tweeted: "Video of assault against one of my constituents absolutely shocking.
"Have been supporting the family since it was first brought to my attention.
"Understand from council that the school have taken strong action. Will be following up to ensure all available support is being given!"
The victim is reported to be a refugee from Syria and a fundraising page has received more than Â£37,000 in donations in less than 12 hours.
Superintendent Steve Dodds, of West Yorkshire Police Kirklees District, said: "We are investigating a report of a racially-aggravated assault of a 15-year-old boy which occurred on playing fields at Almondbury Community School at about 1pm on October 25.
"A 16-year-old boy has been interviewed by voluntary attendance in connection with the incident and we are continuing to progress the investigation."
Kirklees Council said: "Neither us nor the school condone violence in any form and behaviour like this will not be tolerated."