How can anyone comment when you haven't specified the dose or how many "all" of them is.
If you are prescribed Adderall for medical reasons then you are best off taking them as directed, if you abuse them you will raise your tolerance and will likely find your prescribed dose no longer does what you require of it.
I would advise starting low and working your way up, waiting 15 minutes between taking pills seems silly to me, it isn't long enough to know how the drug is affecting you so at that point you can't make a reasonable judgement on whether to take more, 45 minutes to an hour would be a more sensible time to wait and assess how well the dose is working.