Complex sentence: Rajendra Hazra, as well as other scholars, for example, consider "Gaya-mahatmya", which an embedded travel guide to Gaya, to have replaced older sections of the "Vayu Purana" later, but before the 15th-century.
Split into simpler sentences: Rajendra Hazra, as well as other scholars, for example, consider "Gaya-mahatmya", which is an embedded travel guide to Gaya, as a later addition. The "Gaya-mahatmya" replaced older sections of the "Vayu Purana", sometime before the 15th-century.