A:

The built-in filters are very fast!

The built-in global reverb is about as expensive as mixing each sample twice (which is basically free - mixing 64 samples on a modern PC only costs about 1.5% of the CPU).

The built-in low-pass filter is also almost free - on a modern PC, you can low-pass filter 64 samples in less than 2% of the CPU.

Other filters are more CPU-intensive -- using the Chorus filter on 64 samples, for instance, takes about 8% of the CPU. You can use the AIL_digital_CPU_percent function to check the CPU demands imposed by the filter(s) your application uses.