A metric ton is a million grams, 1 megagram or 1 Mg.
1 lb = 0.00045359237 Mg . . . . conversion factor (exact)
2000 lb = .90718474 Mg . . . . . multiply the above equation by 2000
1 short ton = 0.90718474 Mg . . . recognize 2000 lb = 1 short ton
Now, this equation can be multiplied by 15 to get your conversion.
15 short tons = 13.6077711 Mg