Answer : The time required is, 16.1 minutes.
Explanation :
First we have to calculate the amount of heat required to increase the temperature is:


where,
Q = amount of heat required = ?
m = mass
= density of air = 
V = volume of air
C = specific heat of air = 
= change in temperature = 
Now put all the given values in above formula, we get:



Now we have to calculate the time required.
Formula used :

where,
t = time required = ?
Q = amount of heat required = 
P = power = 1500 W
Now put all the given values in above formula, we get:


Thus, the time required is, 16.1 minutes.