I think it depends solely on your circumstances. You must have enough money to back you up and ofcourse the fact of your body needing to heal. But, by all means everyone is different and if they want another child so soon, let them be :)
I do think that Having them so soon has its pro's and con's though:
Such as, the children will be very close and play together perhaps even in the same school together at same time
cons though, the first born tends to get less attention, besides all your attempts to give them equal amounts.
I have a 14 month old son and I am pregnant with my second now, already feeling the bite! eek