How long do I have to wait for the next bus?

下一趟车要等多久才来呢?

About 15 minutes. There is a bus every 15 minutes.

大约15分钟吧。每隔15分钟就有一趟车。

When is the next train?

下班车是什么时候?

When will the next train leave?

下班车什么时候发车?