Deductions & credits

I have a question.
We received an invoice on December 15 Y1 for a 30 days service that we will be taking.

Invoice reads as
For services from December 15 - December 31 Y1 - $ 4000

For services Jan 1 y2 - jan 15 y2 - $ 6000.

Then @ December 31 y1
We should expense only 4000. Am I correct.

January will be expensed in next year Because services are not yet performed for 15 days in January.