Crucial says 32G max and guarantees it.  Even if you install faster RAM, it will downclock to 2400 -- the CPU controls the memory speed.

Dell's specifications say your system will run RAM at 2133 MHz. You should be able to use up to 32 GB.

Don't worry that Dell's specs show a lower maximum of 16 GB. Dell's maximum memory specification is published at the time of system design, based on what they tested. It's not a limitation, so don't take it as gospel. Technology evolves, and often larger RAM sticks and larger drives become available after Dell publishes the specs, and Dell does not generally go back to revise the maximum specs. So, Dell's specs should not be interpreted as limitations or maximums.

Here is Crucial RAM that is compatible with your laptop. While you can use Crucial 2400 MHz or 2666 MHz RAM, it may downclock to 2133 MHz.