My first trip on QR had a 45 minute connection. Plane arrived late, bringing it down to 15, and my connecting flight was right at the far end of the terminal. I still made it though.
Ground staff were nowhere to be seen though. I was first off the plane, travelling in F. Doubt I'd have made the connection if I was in economy.
I've always aimed for 1.5-2 hours since that experience, and have always found that to be the perfect amount of time to get food and/or a shower in the lounge.