I don't mean an offence by this but, It is obvious you not a professional, or a regular comp. I would seriously suggest not getting in over your head early on in the learning curve. Dont simply look at #'s and judge the output or result by them. The install can make great equipment like Sundown sound great or like a kraco system from Kmart. Unless you are going to blurp you system for a comp. the real world result of getting an extra 300 watts out of you 1500d really wouldn't be noticeable. Typically it takes X2 the wattage or cone area to make a noticeabe difference. So the additional strain you put on your electrical system wouldn't be wort the very small improvement in volume if you went to .5 ohm
just my $.02