First of all, it takes 80km per hour and 0.25 hours to arrive, which means that the distance between Party A and Party B is 80*0.25=20km.

Then, the speed when coming back becomes: 80 * (1+0.2) = 96 km/h.

Time used: 20/96=5/24 hours.

So it takes less time to return than to go: 0.25-5/24 hours.

That is, (0.25-5/24) * 60 =15-12.5 = 2.5 (minutes).