I was with you up to this line. What does "0.015 of this amount in proportion to what is the bankroll" mean?

Suppose I deposit 1 BTC. The system registers I am owed 1.19 BTC.

Then someone deposits 0.5 BTC.

How does the 0.015 apply? Do I get 0.015 BTC? (0.015 * 1)? Or half that (0.015 * 0.5)? Or something else?

I guess what you mean is that every hour 1.5% of the bankroll gets paid out to creditors, in proportion to the amount they are still owed.

That seems like a reasonable scheme. It could keep paying out for a long time after deposits dry up, giving a chance for new deposits to arrive.

There was a "rain bot" on Just-Dice which would collect donations and randomly pay out 1% of its balance to random players. That meant that it took a long time to dry up. The payouts slowly got smaller, but someone would inevitably top it up before it ran dry.