It sometimes depends. D:
I have a sparkle dog that takes ages to load cos of her random colourful markings. Also it could be the position you saved in, sometimes when I quit the game in a certain position and I go on her again, I crash. This is because of lag. Try turning off water reflections and view distance, then when you have gotten your game back on, turn them back on! If this isn't your answer, please supply more details so I can figure out the problem.