Tomb of Tal Rasha Runs - Diablo 2 Leveling Guide
The Tomb of Tal Rasha is the best place for you to level up from 15 - 24; these are typically refered to as 'Tomb runs' in the Diablo community and if you're playing on a Diablo 2 mod like Path of Diablo or on regular Diablo 2 at the start of a Ladder it's not uncommon to see multiple public games going with people doing these runs.
For a Tomb run players typically teleport to the Canyon of the Magi and go from tomb to tomb clearing all of the enemies inside. Once all 7 Tombs of Tal Rasha are cleared you start a new game and clear them all again. If you're by yourself (depending on your gear) you can probably start doing these runs at level 16 or 17. At that level though Champ/Boss packs will probably be pretty tough as will the lightning scarabs.
If you're struggling inside of the Tombs of Tal Rasha I recommend clearing enemies outside in the Canyon of the Magi for a level or two, or just avoiding the Champ/Boss packs when you're inside of the tombs. You may have to skip clearing some tombs each run but at least you know the mob density is really good and the amount of travel time between locations is low.
Every 'fake' Tomb of Tal Rasha will have a Golden Chest in the back (pictured above) with a unique enemy guarding it. In my experience most of the fake Tal Rasha Tombs are extremely small, typically a dozen rooms at most with a Golden Chest. The real Tomb of Tal Rasha is significantly bigger, the map typically is too large to fit on your screen without moving it.
Another thing that I noticed (or at least it seemed this way) is that the mob density inside of the real Tomb of Tal Rasha was much higher than the fake ones. Additionally keep in mind that if you're playing on single player you can increase the amount of EXP and drops by setting the players in your game to something higher than 1. Try /players 6 for a decent challenge or /players 8 if you'd like things to be as hard as they can get (but also the most rewarding).
How far away you can be and still get EXP.
While I was power leveling many alts through Tomb of Tal Rasha (and other areas) I spent a bit of time experimenting to determine just how far away you could be from the people killing but still in range of EXP. As you can see in the screen shot I am using third party programs (kolbot) to display monsters on my map, in my experience with this program so long as the monster is currently displayed on the map you'll get EXP for it.
I know that doesn't help regular players since not everyone uses this program but it's useful to mention here since you can see the red X's on my map above, which are the monsters. Along with the blue circle (which is my 'guess' for EXP range) you can see the location of the monsters and try to gauge the real EXP range from there.
Typically what I do is leave my character three or four rooms behind while I go around clearing the tomb. I also try to position them in an area where I can clear multiple directions without having to move them. For those of you out there who aren't power leveling an alt or a friend then you won't have to worry too much about the EXP range since the person will probably be following you closely the whole time anyway. Despite this, I believe it is still useful enough to mention to you.