Did you do anything special to get them running well together?
On my rig jminer runs very slowly alongside eth miner. On its own jminer runs in -30 seconds with eth miner running its like 160s. Did you do anything to get them to run well together?
If you're using windows you can set-up priority for jminer higher:
C:\Windows\System32\cmd.exe /C START "Java"
/high java -jar -d64 -XX:+UseG1GC burstcoin-jminer-0.4.4-SNAPSHOT.jar