ARM Cortex M Power Consumption -- Sleeping with Higher Clock Speeds vs. Lower Clock Speeds
This is very dependent on your exact application, exact MCU and exact circuit. There is no definitive choice between "sleep a lot, run fast" or "run slow all the time" as there are many ways to "sleep" and "run".

Most MCUs have different "depth" of sleep modes. You can sleep with internal 32kHz oscillator, wake up then run from a faster internal oscillator, or start an internal PLL and multiply the oscillator to get higher speed (but the PLL takes time = power to start), you can wake up and start an external crystal (it also takes time and power to stabilize).

Some MCUs have peripherals that can do a lot without using the MCU at all (eg. the PRS in EFM32). If you say that you need a periodic interrupt to calculate something, then you also probably need to get the data in (unless only the internal state matters). Some MCUs can use timers and DMA to trigger the ADC, transfer data and only wake up the CPU when eg. 1000 samples are ready, so you can sleep much more if you just change your application's requirements.

On one project I have worked on, an STM32L011 had best power efficiency when sleeping with a 32kHz internal oscillator and running from internal 2.1MHz oscillator. Don't generalize. If my calculations were more demanding, then perhaps bumping the clock speed to reduce processing time could give better power efficiency (even at the expense of having to wait for the clock system to reconfigure and stabilize).