can use jobs without ecs ? code example

Example: can use jobs without ecs ?

Yes you can. You can put [BurstCompile] over any IJob and it will speed up this job. 
The speed depends on your task. 
If you want to do some benchmarks, be sure to toggle off the JobsDebugger, the Leak Detection and enable Synchronus Compilation for Burst (otherwise Burst Jobs are compiled asynchronously while you are playing the game). Also it helps to use the fast Mathematics Package in your IJobs and using [ReadOnly] wherever you can.