I think 3 basic lands are a little low. All of your Glacial Fortress ,and more than likely your Sulfur Falls , are coming in tapped which is slowing the progression of your deck. and paying 2 life for your Steam Vents and Hallowed Fountain each time may prevent you from reaching later turns in a game.
In playtesting, you only have to play for life maybe 2 times a game, but if you are controlling the board. Then you have life to spare.
I would suggest putting in Detention Sphere
Delver has never had a problem with paying life to maintain control. Gitaxian Probe Gut Shot Dismember for example. paying life to maintain a strong board state is not uncommon and many opponents will be doing the same.
I would suggest heavily against Index .. It's just not a strong card at all. you're better off with think twice in it to help trigger a miracle on there turn. maybe dropping Negate down 1 to fit in an extra miracle or other utility spell, Unsummon or Dissipate perhaps, you have 5 non creature counters currently.
@RhelloZ, Index is very nice in this deck. You set up your Thought Scour and Izzet Charm . That's why I have Feeling of Dread and other spot removal. I can deal with creatures but other spells that pump up the board or wreck my hand, I want to defend against that.