[Python] How can I prevent my snake game from slowing down every time a segment is added?

I'm coding a simple snake game in Python 3 with the turtle module, every time the snake eats the food though it gets a little slower, and eventually the game is impossible to play.

I want to make the speed constant and fast enough that you can play the game without getting annoyed because the snake is moving super slow but I don't know how.

Here is the code I have so far, I still have a few other things to do but just ignore those.

#------------------------------------------SETUP------------------------------------------
#import statements
import turtle
import random

#variables
score = 0
up = True
down = False
left = False
right = False
high_score=0

#background
wn = turtle.Screen()
wn.title("Snake Game")
wn.bgcolor("black")
wn.setup(width = 600, height =600) #set height and width of the screen

#create snake head
head = turtle.Turtle()
head.shape("square")
head.color("green")
head.penup()
head.goto(0,0)

#food
food = turtle.Turtle()
food.shape("square")
food.color("red")
food.penup()
food.speed = "fastest"
food.goto(0,100)

#segments
segments = []
segment_locationsy=[]
segment_locationsx=[]

#create pen to write score
pen = turtle.Turtle()
pen.speed(0)
pen.shape("square")
pen.color("green")
pen.penup()
pen.hideturtle()
pen.goto(0,260)
pen.pendown()

pen.write(pen.write("PRESS SPACE TO START" , align = "center", font=("Courier", 24, "normal")))
#------------------------------------------FUNCTIONS------------------------------------------
# define a function for each direction
#TODO: FIX REPETITIVENESS
def go_up():
global up,down,left,right
if (down != True):
up = True
down = False
left = False
right = False
def go_down():
global up,down,left,right
if (up != True):
up = False
down = True
left = False
right = False
def go_right():
global up,down,left,right
if (left != True):
up = False
down = False
left = False
right = True
def go_left():
global up,down,left,right
if (right != True):
up = False
down = False
left = True
right = False

#create a function to make the turtle move
def move():
if up:
head.sety(head.ycor()+5)
if down:
head.sety(head.ycor()-5)
if left:
head.setx(head.xcor()-5)
if right:
head.setx(head.xcor()+5)

#function to reset the food location
def reset_food():
new_x = random.randint(-280,280)
new_y = random.randint(-280,280)
if (head.distance(new_x,new_y)<20): #make sure that apple doesn't overlap with the snake
reset_food()
for i in segments:
if ((head.distance(i)<20)):
reset_food()
food.hideturtle()
food.goto(new_x,new_y)
food.showturtle()
#function to add to the score
def add_score():
global score
global high_score
score = score + 1
if (score >high_score):
high_score = high_score + 1
pen.clear()
pen.write("Score:" + str(score) + " High score:" + str(high_score) , align = "center", font=("Courier", 24, "normal"))


def start_game():
global up, down, left, right
global score
pen.goto(0,260)
food.goto(0,100)
score = 0
up = True
down = False
left = False
right = False
pen.clear()
game_go = True
segments = []
segment_locationsy=[]
segment_locationsx=[]
head.goto(0,0)
# call function every time screen is updated
var = 0
while game_go:
wn.update()
move()
#assign a key for each function
wn.listen()
wn.onkeypress(go_up, "i")
wn.onkeypress(go_down, "k")
wn.onkeypress(go_left, "j")
wn.onkeypress(go_right, "l")
#reset snakehead when it touches the border, stop movement and reset direction, clear segments
if (head.xcor() > 290) or (head.xcor() < -290) or (head.ycor() > 290) or (head.ycor() < -290):
game_go = False
# add a segment every time it touches food
if (head.distance(food)<=15):
segment = turtle.Turtle("square")
segment.color("green")
segment.hideturtle()
segment.penup()
segment.goto(head.xcor(),head.ycor())
segment.showturtle()
segment.speed("fastest")
segments.append(segment)
reset_food()
add_score()
#segments follow along
segment_locationsy.append(head.ycor())
segment_locationsx.append(head.xcor())
var2 = 1
for i in segments:
i.setx(segment_locationsx[var-5*var2])
i.sety(segment_locationsy[var-5*var2])
if (head.distance(i) < 15): #snake dies if it touches itself
game_go=False
var2+=1
var+=1


#write game over
pen.clear()
pen.pu()
pen.sety(pen.ycor()-50)
pen.write("GAME OVER" , align = "center", font=("Courier", 24, "normal"))
pen.pu()
pen.sety(pen.ycor()-50)
pen.write("press space to restart" , align = "center", font=("Courier", 24, "normal"))

for i in segments:
i.clear
i.hideturtle()


#------------------------------------------RUN GAME------------------------------------------
while True:
wn.listen()
wn.onkeypress(start_game,"space")
wn.update()


I've tried looking this up but just got more confused and couldn't implement anything into my code (if anyone answers this please include a beginner-friendly explanation as to how to fix the problem, thank you!)

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