Let's crisp that argument up a bit.
The Greek word for Advocate here is παράκλητος ("parakletos"), which is a masculine noun. By the rules of Greek grammar, its pronoun and any verbs stating what the subject does also have to be in a masculine tense. Then, since English language only uses "he" or "she" for persons and "it" for things, the translator has to decide from context whether the subject is a "he" or an "it". In this case, the translators decided a priori that the Advocate was a person in John 15:26, so they translated the passage, "He will testify about me". Similarly, the Greek word for spirit is πνεῦμα ("pneuma") and is a neuter noun, so if translated literally, that "whom" in John 14:26 should really be a "which", but the NIV translators decided the Spirit is a "whom".
But, these are good verses, so let's use them. I would argue that the role of an Advocate (or "Comforter") requires a Person, as does the role of "teacher" in John 14:26. Furthermore, since the Spirit "goes out from the Father" and is "sent by the Father", if the Advocate/Spirit is indeed a person, then he/she is distinct from the father. Then the last question would be, "Is the Advocate/Spirit of the same "essence" as the Father and the Son"?