Why doesn't my Pygame game scroll properly?

When I am clicking the arrow keys, in order to scroll my ground and my lucky block, I cant just press the key and it keeps on going scroll. So I need to press the key every second to get a kinda smooth scroll.

from os import environ
environ['PYGAME_HIDE_SUPPORT_PROMPT'] = '1'
import pygame
import config
import spriteSheetLoader as sSL

# Some standard setup variables
scr = config.SCREEN_SIZES[:]
capt = config.CAPTION
clock = pygame.time.Clock()

# load image
sheet = pygame.image.load('img/tiles.png')
sheet = pygame.transform.scale2x(sheet)
tiles = {
    "brown-broken-wall": sSL.loadTileInfo(0, 0),
    "brown-wall": sSL.loadTileInfo(0, 1),
    "lucky-block": sSL.loadTileInfo(0, 24)
}
ground = []
tiles_pos = []
setted = False

pygame.init()

# Setting up our window
win = pygame.display.set_mode((scr[0], scr[1]))
pygame.display.set_caption(capt)

def setup_ground():
    for i in range(15, 22):
        for j in range(0, 50):
            ground.append([j * 32, i * 32, tiles["brown-broken-wall"]])
    tiles_pos.append([14*32, 10*32, tiles["lucky-block"]])
    tiles_pos.extend(ground)

def draw():
    global setted

    win.fill((62, 152, 255))
    if not setted:
        setup_ground()
        setted = True
    for i in tiles_pos:
        win.blit(sheet, (i[0], i[1]), (i[2][0], i[2][1], 32, 32))


    pygame.display.update()

while True:
    clock.tick(40)
    keys = pygame.key.get_pressed()

    draw()

    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            quit()
        elif keys[pygame.K_RIGHT]:
            for i in tiles_pos:
                i[0] -= 15
        elif keys[pygame.K_LEFT]:
            for i in tiles_pos:
                i[0] += 15