just ditch the C rating concept for a second.
the continuous discharge and capacity of an individual cell is multiplied across the parallel pack.
your 30q cell has 15amp continuous discharge and 3000mah capacity.
in your proposed 10s2p pack, the continuous discharge and capacity will be 30amps and 6000mah.
so…30amp is the continuous discharge rate of your 10s2p pack.
i think most would agree that 30amps is a bit low for an esk8, as your motor(s) will easily exceed that during acceleration or goin uphill or both.
if you draw more current out of your cells than what they’re intended, they will for sure heat up and heat will eventually kill your cells prematurely or worst blow up.
so then, if you add an additional cell to your parallel pack, your continuous discharge will go up to 45amp and total capacity to 9000mah.