A better view

As far as I can tell from the image, the deformed leaves are older ones, and newer growth is just fine. If that's so, forget about them.

As for how long to run the soaker, 15 minutes is a very brief time.

To determine how deep and wide the moisture went, probe the soil with a trowel following an irrigation.

This kind of leaf deformity can be caused by a number of insects - aphids, for example - that attack the leaf when it is just beginning to emerge. More common, however, is to see this kind of leaf when the plant is putting out a second surge of growth some weeks or even months after the initial spring flush. I'm not sure if there is any widely accepted explanation for this, but if these leaves have just recently begun to appear that's what's happening. Usually, only a few rather than all of the second flush leaves will look like this. Some varieties of rhododendron are more likely to do this than others. Removing them is fine as they will never assume a normal shape.

Dark green leaves are to be expected - in fact, the preferred coloring with most selections. And the deformity is explained above by akamainegrower.

I agree with jean about the watering duration. Soakers typically emit water at such a low volume that 15 minutes will barely wet the soil surface in most cases. You want the water to penetrate down the full depth of the root ball or at least 8-10 inches. Depending on soil conditions, that could take several hours. Best to do a few test runs at different durations testing the moisture depth after each.