Staging out of Morotai Island, a detachment of the battalion landed on Muara Island on 10 June 1945, disembarking from US-operated LVTs and securing the island without opposition, while later, other elements from the 2/15th were put ashore on the peninsula around Brunei Town, as part of Allied operations to secure northern Borneo. While the main Australian force advanced towards Kuching and the oil fields around Seria, two companies of the 2/15th served as a "floating reserve" for the 2/13th Battalion's landing around Lutong, while the main body of the 2/15th subsequently moved inland towards Limbang, and began patrolling along the Limbang and Pandaruan Rivers that forked inland from the bay, using landing craft for mobility, and securing several small villages around the edge of the bay. Limbang was taken on 18 June, and two days later the two detached companies rejoined the battalion. Subsequently, several engagements were fought with the Japanese during patrols in June and July, but these were mainly small-scale; two members of the battalion were killed in an ambush around Brunei in late June, the heaviest fighting occurring in early July, when a patrol killed over 20 Japanese in a short but sharp encounter. By the end of July, a draft of 170 long-service personnel were released to return to Australia in early August, just as the war came to an end. Casualties for the 20th Brigade were light; the 2/15th suffered five battle casualties during its last campaign, two killed and three wounded.