NSURLSession with WatchOS 2.2 very slow

I try to download some JSON data from a web server with NSURLSession in a WatchOS 2.2 app. The same code that runs flawlessly on the iPhone itself, takes forever on the watch (using the simulator).

I checked out this example: https://github.com/shu223/watchOS-2-Sampler, which has a function to download and display an image via NSURLSession, and it has the same problem.

The code of this example is:

    let url = NSURL(string:"https://pbs.twimg.com/profile_images/3186881240/fa714ece16d0fabccf903cec863b1949_400x400.png")!
    let conf = NSURLSessionConfiguration.defaultSessionConfiguration()
    let session = NSURLSession(configuration: conf)
    task = session.dataTaskWithURL(url) { (data, res, error) -> Void in
        if let e = error {
            print("dataTaskWithURL fail: \(e.debugDescription)")
            return
        }
        if let d = data {
            let image = UIImage(data: d)
            dispatch_async(dispatch_get_main_queue(), { () -> Void in
                if self.isActive {
                    self.image.setImage(image)
                }
            })
        }
    }
    task!.resume()

Playing around with it, I figured out that if I change the code to

    let session = NSURLSession.sharedSession()

it works fine.

However, I cannot use this in my app because I need to setup delegates.

What can I do to get it working?