Since you say 100% PPS - that means you keep the transaction fees.
Since July last year, that has been around a 1% fee - yes you are lying saying there is no fee at 100% PPS
So using 1% as your fee, the calculation for your necessary reserve is simply:
12.5 x 6.9078 / (2 x 0.01) = 4317.375 BTC
and using a US$ conversion rate (today) of 1BTC = $3,500 that's about $15.1 million
Dear Kano,
We’ve been waiting for your reply and are glad to greet you at our topic.
Firstly, would like to mention that we do have our application store that brings us profit (there is more than 1% we do gain by simply providing the services). At a certain point we will add the PPLNS model to lower all the possible risks.
Furthermore, we are going to use a different from other pools monetization model at the SigmaPool. Creating a pool was just the first step - more to come.
Despite the fact that we already have faced the bad luck times, we are proud to declare that we managed to keep the payouts regular and stable (thanks to our reserves), and we have the best community (where we will be glad to see you and every new miner) that can prove our stability and the level of our services.
Lastly, understanding that we haven’t given a complete answer to your question, we would like to note the fact that pretty soon we will be able to prove that we do have the funds required to sustain the stable PPS payouts (and yes, we do have more than 2000 BTC behind us).
P.S. The 1% fee you are talking about is not a fee - it is the only way to make a PPS method not going broke without touching miner’s earnings. We do believe that giving miners 12.5 BTC per block is more fair than giving them 1% and taking 3% away.