Answer:
Yes, the difference in age and maturity level is to large. And the 15 year old is under the age of consent and there could be legal issues if any sexual contact occurs.
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Yes this could be looked at as pedophilia being the younger is under the Age Of Consent in most Countries.
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If they have sex, it is probably legally defined as rape.
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Added: If the word "dating" is being used as a substitute for "having sex with" it is going to illegal. Even in the states with the most liberal statutory rape laws the age difference is too great to qualify for BF/GF "consenting" relationship.
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Yes it's a minor and a adult. If you have sex you go to prison for statutory rape.