How to adjust the time for reading values for a gas sensor mq3

/* MQ-3 Alcohol Sensor Circuit with Arduino */

const int AOUTpin=0;//the AOUT pin of the alcohol sensor goes into analog pin A0 of the arduino
const int DOUTpin=8;//the DOUT pin of the alcohol sensor goes into digital pin D8 of the arduino
const int ledPin=13;//the anode of the LED connects to digital pin D13 of the arduino

int limit;
int value;

void setup() {
Serial.begin(115200);//sets the baud rate
pinMode(DOUTpin, INPUT);//sets the pin as an input to the arduino
pinMode(ledPin, OUTPUT);//sets the pin as an output of the arduino

void loop()
value= analogRead(AOUTpin);//reads the analaog value from the alcohol sensor's AOUT pin
limit= digitalRead(DOUTpin);//reads the digital value from the alcohol sensor's DOUT pin
Serial.print("Alcohol value: ");
Serial.println(value);//prints the alcohol value
Serial.print("Limit: ");
Serial.print(limit);//prints the limit reached as either LOW or HIGH (above or underneath)
delay(100) ;
if (value > 300){
digitalWrite(ledPin, HIGH);//if limit has been reached, LED turns on as status indicator
digitalWrite(ledPin, LOW);//if threshold not reached, LED remains off
Here I would like my sensor to take the value for every 15 mins,instead of continuous reading.
How can that be achieved?

Get rid of those delays and use millis() for timing.

Non-blocking timing tutorials:
Several things at a time.
Beginner's guide to millis().
Blink without delay().