Is it possible to implement timeheader with 3 hours as a part, but cell with 15 minutes as a part

Yes, this is possible. If the built-in time header units don’t work for you, you can define custom segments, as described in the following tutorial:

• JavaScript Scheduler: Custom Time Header Segments

The time header is set to an area every three hours, and the lower grid area is set to an area every 15 minutes. At this time, the cross hair does not take effect for every hour in the header

Unfortunately, the crosshair is only supported by the built-in time header groups.