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
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.