Complex sentence: Unable to convince Lanshi, Wenzong talks to her parents and eventually convinces them to agree because Wenlong has been gone for 15 years, and a wedding date is fixed for a few days' time.
Split into simpler sentences: Unable to convince Lanshi, Wenzong talks to her parents and eventually convinces them to agree, reasoning that Wenlong has been gone for 15 years. A wedding date is fixed for a few days' time.