Don't know about 15 but certainly 30 (0.975^30 = 0.468) see my previous post.
It's a ll short term versus long term. I can take short term variance but I can appreciate someone owning a small business might not.
Keep in mind to that there is no economy for bit-coins... I can not buy my products from my suppliers with bit-coin, I can not pay rent with bit-coin, I can not pay the power company with bit-coin...
But we can buy tea with Bitcoin, and that's a step in the right direction.