1. 意思：指十五小时整点，即24小时制下的下午3点钟。

How to read: [ˌθɜːtiˈfɪv]

Usage: Used to indicate the time of day, specifically 3 o'clock in the afternoon in a 24-hour clock system.

Example sentences:

1. It's already fifteen o'clock, we should start heading home.

现在已经是十五点了，我们应该开始回家了。

2. The meeting is scheduled for fifteen hundred hours, don't be late.

定于十五时开始，不要迟到。

3. We'll meet at fifteen hundred hours in front of the coffee shop.

我们将在咖啡店门口见面，时间是十五时。

4. The train will depart at precisely fifteen o'clock, so make sure you're on time.

火车将在十五点整准时发车，所以确保你准时到达。

5. I always take a break at fifteen hundred hours to have some tea and snacks.

我总是在十五时休息一下，喝点茶吃些小吃。

Synonyms and usage:

1. Three o'clock: another way to say "fifteen o'clock" in a 24-hour clock system.

2. Three PM: used in a 12-hour clock system to indicate 3 o'clock in the afternoon.

3. 1500 hours: military time used to indicate 3 o'clock in the afternoon.

Editor's summary:

In summary, "fifteen o'clock" refers to 3 o'clock in the afternoon in a 24-hour clock system. It is often used as a formal or military way of indicating time and can be replaced by "three o'clock" or "three PM" in a 12-hour clock system. It is important to pay attention to the context and use the appropriate time format when referring to a specific time of day.