Use code tags, so your code looks like this, and we can actually see the two different codes in separate blocks:
for (pos = 90; pos >= 180; pos -= 1) {
myservo.write(pos);
delay(15000);
}
This part will be running very slowly (moving 1 degree per 15 seconds), it's going to take an awfully long time for this loop to finish - about 270 hours - and in the meantime the servo will start doing all kinds of craziness due to undocumented behaviour of the servo.write() function for position values >200.
How are the buttons wired?