0.15 on Steam wallet

Ummmmm... Yes you will.

You can use your Steam Wallet to pay off part of a purchase and pay for the rest of it with your credit card or whatever.

I've never used my steam wallet, and probably never will, because I'm "modern and hip".

Unless there isn't a chance that you will ever increase your steam wallet again, just save it instead of buying useless trash just to clear the wallet.

If you put money in your wallet you don't own the money anymore. You just "buy" x "SteamDollar" and the money belongs then to Valve (and I think it is the same for other companies). The Steam wallet is useful when you use paysafecards or make micro payments on Steam. You could anyway just use PayPal/Credit card/whatever to pay the rest of the game or wait until you get the enough 15 cents to buy Fortix and give it away here.