You must be setting targets differently on M5 charts, I think, from how you feel you’d set them on M10 or M15 charts, then? The levels prices reach are clearly not determined by the periodicity of charts we select.
Again, the levels prices reach will not be changed by looking at them on a different chart.
If you’re using indicators to select your entries and/or targets, that’s another matter.
In general, indicator signals tend to be more reliable on longer time-frames, and produce higher win-rates, but that doesn’t necessarily mean that they also produce higher overall profits, because reliability (win-rate) and profitability are two different parameters.
Many traders feel that what they mistakenly refer to as “noise” on lower time-frames is reduced on higher time-frames.
In any case, I would suggest that only [I][U]testing[/U][/I] can possibly answer your question with confidence: you probably need to compare the outcomes of 300 trades on each time-frame (not forgetting to allow for trading frequency as a parameter, of course, in calculating the profitability of each). Anything else is going to be only a [I]guess[/I], at best - and that’s clearly no basis for trading decisions.
(For what it’s worth, if anything, personally I would test M10 charts before M15 charts, if you’re currently using M5 charts and wanting to know whether “slower is better”.)