Complex sentence: It later became part of Highway 7 and Highway 15 before the western leg of Highway 417 was completed, after which it was known for a time as "Old Highway 7 & 15".
Split into simpler sentences: It later became part of Highway 7 and Highway 15 before the western leg of Highway 417 was completed. After which it was known for a time as "Old Highway 7 & 15".