Me . don't answer if you will be toxic. ☣

15 = 3² +2(7-4)

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The above expression includes operations of

The exponent is 2.

I know the value of this expression is 15 because

Try this:  3*125^(1/3).  Note that 125^(1/3) = 5 and that the original expression is now 3*5, which = 15, as required.