Your time in jail is a punishment for what you did wrong. If the game would just give you a 2 sec loading screen the whole jail/law thing would be useless.
Your problem is propably your CPU. If you fast travel the game is still running in the background. It speeds up all the npc actions wich is very hard for your pc because the stuff that the pc has to calculate in normal time has to be done 2, 3, or 4 times faster (depends on your setup). I guess the same thing happens when you are in jail. because i was in jail for 8 days and it took maybe 50 seconds.