How do people level up so fast?

Then what level should I start going to Sand Rat/Scorpions.

Also, the transportation time seems so long. 7 minutes to get there from Vic Island + they do high damage. How would that be a good choice?

You do know that you can go almost anywhere from Pantheon, right? Also, lol @ judging training spots by their distance from Victoria Island.

This is the benefit of Pantheon. Pick a level and try it out. Try the mob. If it doesn't work out for you, just go back to Pantheon (hell, Karcasa near Ariant even warps you to Victoria for a measly 10k). Warp somewhere else. Simple.

 This is your gold mine. Right here.

 Getting back to Victoria from places

• Mercedes can warp back to Elluel with a 30 minute cooldown. This is their link skill too, so you can give this benefit to any of your characters with a level 70 Mercedes.
  
• Kaiser and Angelic Buster get free warps directly to Pantheon with a 10 minute cooldown.
  
• Victoria: Nope.
  
• Orbis: Victoria is two minutes away by plane.
  
• El Nath: Orbis Tower. Two minutes away by plane.
  
• Ludibrium: Ride down to KFT, then to Aquarium, then to Orbis Tower, and back to Orbis. Two more minutes and you're there.
  
• Leafre: If you're here you can afford a 30k magic seed back to Ellinia.
  
• Magatia: Two minutes away by plane.
  
• Mu Lung: You can fly to Orbis, or go to Herb Town, then Aquarium, then Orbis Tower and Orbis.
  
• Ariant: Karcasa can warp you back to a random Victoria town for 10k.
  
• ANYWHERE if you like: Warp to NLC via Dimensional Mirror and take a subway train back to Kerning City. If you really want to. This generally takes longer.