Well for 15 mins only it seems little tricky as no one will willingly take the pain of extracting first 15 mins data for u.
so lets talk alternate scenario,
Search for how to extract data from zerodha kite on this forum.
Get that R file.
Use it with kite login as directed.
Get cash market data as much as u want. Yeah, only catch is u will get full day data. u will need to extract first 15 mins on ur own..
Good luck..