Adsense, how much would ~15,000 unique visits (20,000 pageviews) be worth?

That's hard to make estimation since we dont really know the CPC and CTR
Just try on it and you will know the result. If you dont satisfy with the earning, you can just remove the ads after

 

Its important to note the type of traffic. Social media sites move lots of visitors but have a very low click through compared to search visitors. If you find a consistent formula for bringing in lots of social media traffic, a cpm advertisers would be your best bet. If its search, adsense or something similar is best.

 

I think you should use CPM to earn good amount
If you get 50,000 page views a day you revive $50-80 per day it means you earn $1500-$2000 per month

 

>that depends on your adsense placement

Totally agree here. With ads just placed haphazardly in the sidebar, you'd be looking at pennies. But optimized positions and sizes and you could be up at $15 RPM, based on your numbers up to $300.