Why is mean_sweep_response so slow

Hi guys. I’m pretty new to Allen Brain Map. I’m currently just trying the tutorial for SDK right now. However, it seems like it take forever to get population response:

from pathlib import Path
from allensdk.brain_observatory.natural_scenes import NaturalScenes
output_dir = '.'
from allensdk.core.brain_observatory_cache import BrainObservatoryCache
boc =  BrainObservatoryCache(
    manifest_file=str(Path(output_dir) / 'brain_observatory_manifest.json'))
dataset = boc.get_ophys_experiment_data(541206592)
ns = NaturalScenes(dataset)

The last line is taking forever. Is this normal?