We also probably spent a sizable chunk of TAM to pay for the transfer fees of Brillant and Mata so we don't really know how much is left.
No, TAM only applies when the players original salary is above the maximum salary threshold for that year. ($457,500 is 2015). The only player that fits that is Mix, and at $761,250, that means that we must have uses a little over $300,000 in TAM for him this year. Each team was given $800,000 in TAM to start and $100,000 every year after for the next 5 years (though we could have traded for more TAM). Based on that, we have $750,000 in TAM left if we sell/trade Mix (I'm pro-rating 2016's $300,000) $800,000 + $100,000 - ($300,000/2). Moreover, any new player we sign and use TAM for can't originally earn more the $1,000,000 to qualify unless he starts as a DP and we buy him down. Since we don't have an open DP spot, that's not an option at the moment.
PS, reading this I think I have to make some adjustments to my cap analysis, changing Mix's cap hit and tracking TAM remaining.