Since you are able to use ADB and have busybox you may be able to use a shell script that allocates memory until it's exhausted.
refer to Write a bash shell script that consumes a constant amount of RAM for a user defined time
ripped from that answer:
#!/bin/ash
echo "Provide sleep time in the form of NUMBER[SUFFIX]"
echo " SUFFIX may be 's' for seconds (default), 'm' for minutes,"
echo " 'h' for hours, or 'd' for days."
read -p "> " delay
echo "begin allocating memory..."
for index in $(seq 1000); do
value=$(seq -w -s '' $index $(($index + 100000)))
eval array$index=$value
done
echo "...end allocating memory"
echo "sleeping for $delay"
sleep $delay