Can I mismatch different ram capacities?

So I managed to find 2x8gb 1600mhz kit of hyperX beast. I wonder if I could add these with my 4gb sticks for total of 24gb?

OTHER THING. My existing memory is 2133mhz but it has an xmp profile with exact same speed, voltage and timings as the ones im looking forward to buy. Would they work normally with the same xmp profiles?

Motherboard: Asus Z97-K

sry about bad english im tired =)

Yeup. However its more than likely that you will have to use the ram speed of your slowest ram kit.

You MIGHT be lucky enough to overclock the slow ram to match the faster kit, but no guarantees.