As I say, I don’t scalp, so I don’t want to be too specific; any recommendation I made would be guesswork.
However, the overall object of any indicator is to quickly give you information about the market over a relevant time-frame. That last part, ‘relevant time-frame’, is key. For scalpers, the relevant time-frame is usually much shorter than for daily traders.
Take the RSI, for example. The standard setting on that is 14, which means on the M15 it is taking into account market movements from 3.5 hours ago. Do you actually care what the market was doing three and a half hours ago? If yes, and your strategy is based around that, then the setting is probably fine. But if, as I suspect, you are looking to trade movements and hold positions over a much shorter timescale, then your indicator is probably getting bogged down with old news.