Oh you don’t go through Westfield, too many people (and ice cream temptations). Jubilee line, Westfield exit, past the bus station, turn left down the service road, and in the back entrance. About 600metres and never anyone in the way.
Which is what I did. Never stopped. Set off at 1302. Now I like to think I'm no slouch when it comes to activity (School cross-country colours, 1971

), and only had limited time
International (entrance) at 1314, shot at moment of arrival, outside gateline. So 12 minutes if done at a good stride. Add one more down to the platform.
Couple of points. There appears to be no signage whatsoever within the main line station pointing to the international station. Presumably you are expected to take the DLR (although that's not explicitly signed as such either). The first such sign I noted is outside the Westfield gateline. And it points you through the shopping centre. And had I had luggage it would have taken a sight longer. Oh, by the way, it was raining (well, it is a bank holiday weekend).
Separately, I noted later the signage between the stations is notably lacking. In particular the sharp dogleg inside the shopping centre towards the international end has nothing at all. Although it seems envisaged as a walking route due to the couple of signs, anyone not familiar with things would be completely lost.
Meanwhile, I blame you for making me think of the ice cream on the "shorter" route (because I think in metres it's shorter than the outside route) back through the shopping centre
and the most bizarre of all at a stall a bit further along

this extraordinary model 0-6-4ST, clearly not designed by a mechanical engineer, just out on open display on the London tourist trinkets stall, among the plastic policemens' helmets and the supposed telephone boxes. I didn't ask how much it was.