"十5" in Engpsh can be written as "15." It is simply the number fifteen in Engpsh.
There is no specific origin for the number 15 in Engpsh. It is a basic numeral used in mathematics and everyday counting.
Example sentences in Engpsh:
I have 15 apples in my bag.
The bus will arrive in 15 minutes.
The temperature is 15 degrees Celsius.
Translation in Chinese:
我的书包里有15个苹果。
公共汽车将在15分钟内到达。
温度是15摄氏度。