Some examples are time consuming. I think we should try to simplify them to make these examples more friendly to users and CI.
Examples > 60s (from https://circleci.com/gh/scikit-learn/scikit-learn/50704):

• plot_coin_segmentation.py: 4.6e+02 sec
• plot_iterative_imputer_variants_comparison.py: 1.9e+02 sec
• plot_rbm_logistic_classification.py: 1.5e+02 sec
• plot_pca_vs_fa_model_selection.py: 1.2e+02 sec
• plot_image_denoising.py: 1.1e+02 sec
• plot_digits_pipe.py: 80 sec
• plot_compare_reduction.py: 69 sec

See #13379 #12929