Matthew $15M per year for 3 years. They HAVE to hit the league minimum in salaries. 2015/16 won't be difficult, but 16/17 the salary cap (and the salary floor) will skyrocket. Next offseason every single team in the league will have tons of money to spend. So they either pay a ton of money to a guy this year and have him locked up for a few years, or they'll have to vastly overpay guys next year. Guys that may not be anywhere near as good as Matthews but make the same or even more. Does that make sense?
I know they'll have to re-sign Gobert, Hayward, and Exum in a few years and that will take up a lot of their salary. But if a guy is willing to come to Utah this year, it may be the time to take a chance on him. The risk is high with Matthews because of the injury, but $15M may look like a bargain in a year like Hayward's contract does right now.