well at the minute ive found he took part in the amiens offensive and the closest ive got is queant which is 4.9 miles from the cemetary but if you can get the trench map 57c nw4 then will be able to pinpoint exactly where the 15th brigade were
On 21 August, the British Third Army (Byng) to the north of Rawlinson and the First Army (Horne), even further north, joined in as the attack was renewed. The French Tenth and Third Armies also attacked again. In response to a significant advance by the British First Army, Ludendorff ordered a general withdrawal along the 55-mile front. He came under further pressure as the Anzacs advanced across the Somme on 30-31 August, taking Péronne and Mont St Quentin. Near Quéant, on the northern flank, the Canadian corps broke through on 2 September.
In these unfavourable circumstances the Germans, who had suffered heavy losses, were forced, on 3 September, to retire to the Hindenburg Line, their starting point in the March offensive, bringing the whole operation to a close. By 10 September, the Allies had closed up to the new line. The Amiens salient had been eliminated in a major Allied victory that finally convinced Ludendorff of the need to end the war. Haig, who had used all his available reserves, was unable to exploit the British victory further.
Source
An Illustrated Companion to the First World War by Anthony Bruce