Outgoing calls minute reminder
As Firelord confirmed this for stock Android, you might not need Tasker for that at all – your dialer probably supports this natively:

Open the Dialer, then check its settings. My dialer has there (in German, so don't take my translation literally):


vibrate when answered (additionally, also when hanging up or there's another incoming call)
vibrate every minute (15 seconds before it's up)


I'd say that's pretty close to what you're after – just keep the "vibrate when answered" off and tick the "vibrate every minute", and it's even a perfect match. No need for any additional app, if that's all :)