30mg seems to be the initial dose for adults and children source. So you could start af low af you want, but you might need to increase dosage over time to get any effect.
If your doc signed off on any dosage below 30 and you are afraid of a strong reaction, you could start as low as 10 or 5mg, but most ækel wouldn't experience much.
If you have several capsules you could start very low and increase until you fell an effect.
Do not exceed the doctors recommendations and give each dose a day or two (you ingest a given dosage for one or two days) to affect you.
I am not a doctor, so stick to what doc says, but the smallest dose of Elvanse I could five was 20mg as a maintenance dose.
I would like to add that you are unlikely to feel much at those doses, but you safely start low and go up until you feel an effect.
Furthermore, not everyone experience net benefits from medication, so you shouldn't increase the dose if you feel bad.
Finally, I am not a doctor, neither are most other people on here so consult your own doctor the moment something feels off