How to choose alternative crystal/resonators for arduino

I would like to change the frequency of the system, and looking for alternative resonators.

I found the resonator on the nano is a 16MHz 15pF one. If I replace it with a 8MHz one, for example, should I choose a 8MHz 15pF one? Is the 15pF cap value critical for this? Or it doesn’t matter too much?

The capacitance changes the frequency slightly. Of it is too mismatched the oscillator may have problems to start.

Smajdalf: The capacitance changes the frequency slightly. Of it is too mismatched the oscillator may have problems to start.

So, I guess there are some math to get the exact frequency if the cap value is different. So can I assume, if I want to be exactly 8MHz, it is better to choose a 8MHz 15pF one over 8Mhz 12pF one, for example?

joedodo: So, I guess there are some math to get the exact frequency if the cap value is different.

AFAIK crystal tuning is more a guesswork than exact math. Since there is capacitance of the traces and pins the real capacitance is not known anyway.