Slitherine

I just want to know cause when its not transfered i may need to buy units in my current campaign(39) taking them to the next dlc campaign.

Yes it is, thankfully

Often the DLC have different routes through the campaign. You can play both routes, and then when you load the next campaign it will give you both options to carry forward the better prestige.

The only exception to this rule is when you import a CORE from DLC 1941 into DLC 1942/43 West, your prestige is reset and you are also forced to leave all but a few (8 if I remember right, not including SE units) behind. This was done as a reset button, to provide a better atmosphere to the smaller scale battles that dominated the conflict on the Western Front, unlike some of the gargantuan engagements on the East Front.

9 units + SE