Difference in increment & decrement loop execution speed
Comment out these 2 lines

Serial.print("the value is=");
Serial.print("\t");


And report back on the speed difference.
Why not add a reading of micros() before and after each loop and see how much difference there really is?  All time variables are unsigned long.

startTime = micros();
// your loop
endTime =  micros();
duration = endTime - startTime;
Serial.println (" "); // line break
Serial.print ("duration in uS = ");
Serial.println (duration);


I edited to add some missing )s and a 2nd line break.