can parents press charges on a 22 year old guy if the girl is 15 but the girl denies ever having sex?

Parents are within their legal authority to file a complaint with police against any adult that may be pursuing their minor child illegally, contributing to the child's delinquency, or if they have reason to believe their minor child is the victim of a criminal act perpetrated by the adult. Only a state prosecutor can determine whether charges will be filed against the 22 year old and this is determined through an investigation.

Ohio no longer uses the term "sexual penetration" in the law, but now uses "sexual conduct" which is defined below:

2907.01 (A) “Sexual conduct” means vaginal intercourse between a male and female; anal intercourse, fellatio, and cunnilingus between persons regardless of sex; and, without privilege to do so, the insertion, however slight, of any part of the body or any instrument, apparatus, or other object into the vaginal or anal opening of another. Penetration, however slight, is sufficient to complete vaginal or anal intercourse.

§ 2907.04. Unlawful sexual conduct with minor.
(A) No person who is eighteen years of age or older shall engage in sexual conduct with another, who is not the spouse of the offender, when the offender knows the other person is thirteen years of age or older but less than sixteen years of age, or the offender is reckless in that regard.
(B) Whoever violates this section is guilty of unlawful sexual conduct with a minor.
(1) Except as otherwise provided in divisions (B)(2), (3), and (4) of this section, unlawful sexual conduct with a minor is a felony of the fourth degree.