Help, is 15 watts p/c enough for a small room

I need a vintage amp / receiver for my den which is about 12' x 12' w/ 8' ceiling. Does anyone have an opinion about w/p/c ? Looking at a nice Pioneer sx 450 on ebay for $96 which incl. shipping. 15 wpc
Depends on what you mean. It will be great for background or with horns.

If you want to dance to it, probably not.
Yes, but 12 X 12 is a BAD sounding room to begin with! A pair of Heresy's will play loud enough to cause permanent deafness with 15 watts - but do you really want to lose your hearing?
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Nice sounding unit, for what it is. Is this den system going to be your main listening room ? As stated above : Speaker sensitivity, impedance, listening levels, and the kind of music listened to, such as full, all out orchestral, disco, reggae, and some others, will determine the power required for a particular listening situation. The 1st watt is the most important, as far as cleanliness. And if you have a speaker that does not reproduce the last octave, your receiver will work a little less hard, as bass uses up a bit more power. Enjoy ! MrD.
I would also like to add, that these receivers, and other Japanese audio equipment from the mid 70s, were cheap several years ago. But now, they are demanding high dollars. Most need a good cleaning, and some require a rebuild / restoration. This was the bottom of Pioneer’s line, and even if it is mint, it is old. Just a caution in the wind. Good luck.
Ive owned quite a few vintage recievers and agree it depends on what you are looking to get out if it. If you are looking for a background music maker, the Klipsch Power Gate is a great sounding integrated for the money. Hypex 50 wpc amp, bluetooth, usb and optical input, 2 analog inputs and built in play-fi streaming.

$150 bucks shipped.
Having owned this receiver I'd say it is under-powered when I used Energy Xl-16 spks. I'd personally would pass at that price. I once sold this receiver at a stereo shop I worked at a long time ago. Compared to a Harmon Kardon 330i, the difference in power was night and day. The HK was 20w per channel if I remember correctly. I'd look at something else. Prices are really going up on Ebay and shipping is expensive. Hard to find the deals. But they are still out there, just not as plentiful. 
I used to have that same receiver along with a Technics turntable and some cheap off brand speakers:)It sounded fine at reasonable volumes in larger rooms than yours.Like others have mentioned,pair it with efficient speakers.
Get that new NAD 3020 with the Class D output stage. Avoid that ancient Pioneer!
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Wow thank you everyone! It's just for background music while I work or to test the condition of LP's. Not my main listening room. Main room is about 30 x 33 ,w/  Pioneer SX-980 & Klipsch Forte ii's, not looking for anything like that at all. Main room has a lot of glass & tile so the Klipsch are a little bright sometimes, that's another of many problems. 
I have circa 1968 GE bookshelf speakers for the den, not sure if they work but can get some decent Klipsch on ebay for +/- $100 I think. I will look at the Harmon Kardon 330i and Klipsch power gate, also found a cleaned up, working Pioneer sx-680 on e-bay for $80, might do that, shipping is $55. Thanks again everyone for the help !
Ok, done. Bought the $80 Pioneer sx-680, @ 30 wpc, thanks for talking me out of the 15 wpc options. Hooked up the 50 year old GE bookshelf speakers and the 'revived from storage' Onkyo cp-1020f turntable and surprise, I'm blown away by the full, rich sound, clear highs, little thump from the lows and fantastic mid range that I would love to hear from my Klipsch Forte ii's downstairs. All for 80 bucks, can you belive it? Highly recommend any of these components. This could turn out to be a fun hobby :)