LAX_LHR, firstly it takes 20 minutes from J3 to DSA at quiet times, going the speed limit - I do the journey several times per week.
Secondly, try doing the journey at rush hour (after 4pm going to DSA or before 9.30am coming from DSA), and it will easily take 30-40 due to the traffic on Bawtry Road through Bessacarr.
When the new road is built, the journey it will about 8 minutes from J3 to DSA.