If I'm any kind of proof, I'd say that yes, slow comics have a definite chance here on Tapastic!
I'm slowly inching towards 200 pages, and things have been fairly slow paced so far, but I seem to have enthusiastic readers nonetheless. And I get new readers regularly, despite the size of my archives!
I think that with slower-paced comics, the key thing is to make readers feel invested in the characters. With faster-paced comics, you can focus more on exciting set-pieces and action, but for readers to really care enough to read all your slow buildup, they need to give a damn about the characters it's happening to. Make them care. You have the space; give your characters depth and complexity. Give them secrets to keep, tough choices to make, obstacles to confront, even if they aren't big action-packed extravaganzas.
... at the same time, it's also important to remember that you do need to have something happening. Big establishing shots of environments, and lots of silent panels can be fun - I use them a lot - but you can't just let your character spend three pages slowly making breakfast for themselves, unless they're also doing something interesting. Like having an internal monologue, or actively avoiding something else because they're anxious, or whatever. Make the panels count towards something.