large amount of lag on shooting

#space invaders

import turtle
import time
import os
import math
import random



#setup screen
wn = turtle.Screen()
wn.bgcolor("black")
wn.title("Space Invaders Turtle Edition")


#draw border
border_pen = turtle.Turtle()
border_pen.speed(5)
border_pen.color("white")
border_pen.penup()
border_pen.setposition(-300, -300)
border_pen.pendown()
border_pen.pensize(3)
for side in range(4):
    border_pen.fd(600)
    border_pen.lt(90)
border_pen.hideturtle()

#Create player
player = turtle.Turtle()
player.color("blue")
player.shape("turtle")
player.penup()
player.speed(0)
player.setposition(0,-260)
player.setheading(90)

#create the player's weapon
bullet = turtle.Turtle()
bullet.color("yellow")
bullet.shape("arrow")
bullet.penup()
bullet.speed(1)
bullet.setheading(90)
bullet.shapesize(0.3, 0.3)
bullet.hideturtle()

bulletspeed = 20

#define bullet state
#ready - ready to fire
#fire - bullet is firing

bulletstate = "ready"

#player movement
playerspeed = 15

def move_left():
    if(player.xcor() >= -270):
        playerX = player.xcor()
        playerX -= playerspeed
        player.setx(playerX)

def move_right():
    if(player.xcor() <= 270):
        playerX = player.xcor()
        playerX += playerspeed
        player.setx(playerX)


def shoot():
    global bulletstate
    #Declare bulletstate as global if it needs to be changed later
    if bulletstate == "ready":
        bulletstate = "fire"
        #Move bullet to just above player
        x = player.xcor()
        y = player.ycor() + 20
        bullet.setposition(x, y )
        bullet.showturtle()


def isCollision(t1, t2):
    distance = math.pow(t1.xcor() - t2.xcor(), 2) + math.pow(t1.ycor() - t2.ycor(), 2)
    if distance <15:
        return True
    else:
        return False


turtle.listen()

turtle.onkey(move_left, "Left")
turtle.onkey(move_right, "Right")
turtle.onkey(shoot, "space")





enemyspeed = 1

#choose number of enemies
number_of_enemies = 5
#create list of enemies
enemies = []

#add enimies
for i in range(number_of_enemies):
#create enemies
    enemies.append(turtle.Turtle())

for enemy in enemies:
    enemy.color("red")
    enemy.shape("circle")
    enemy.penup()
    enemy.speed(0)
    x = random.randint(-200, 200)
    y = random.randint(100, 250)
    enemy.setposition(x, y)


#main game loop
while True:


    #time.sleep(.001)

    for enemy in enemies:
        #move the enemy
        x = enemy.xcor()
        x += enemyspeed
        enemy.setx(x)

        if enemy.xcor() > 280 or enemy.xcor() < -280:
            enemyspeed *= -1
            for e in enemies:
                y = e.ycor()
                y -= 40
                e.sety(y)


        if isCollision(bullet, enemy):
            #reset bullet
            bullet.hideturtle()
            bulletstate = "ready"
            x = random.randint(-200, 200)
            y = random.randint(100, 250)
            enemy.setposition(x, y)


    #move bullet
    if bulletstate == "fire":
        y = bullet.ycor()
        y += bulletspeed
        bullet.sety(y)

    #check to see if bullet reached top
    if bullet.ycor() > 280:
        bullet.hideturtle()
        bulletstate = "ready"



    #reset enemy
        enemy.setposition(-200, 250)

    if isCollision(player, enemy):
        player.hideturtle()
        enemy.hideturtle()
        print("Game Over")
        exit()