Vacuum question!

Hi!

I have a question about vacuum! I just got help from a friend to measure the vacuum on the engine.
The thing is we got 15 inches per mercury! I think thats alot and i wonder what may cause it!?

The engine is a 340 stroked to 416cui. The cam is a comp cams mechanical cam with 280/300 in/ex, 239 and 242 @ .50. The lift is 534/540 with 1.5 rockers. The lobe separation is 112 degrees with 4 degrees advance ground in!
The valves are 2.08/1.65.
The distributor is a mopar performance with a MSD 6AL box. Timimg is set 18 degrees to 1200 rpm and then from 1200 to 1500 is increases from 18 to 38 degrees! The carb is a Holley 750 which has been properly adjusted! Im about to test with a Carter Competition 750, thats why we started mesuring!

The rest of the engine is a mopar 4" crank. Mopar M1 intake, not ported! Mopar commando heads stage1 that are converted to open chamber heads. The pistons are KB with -26.5 cc´s. TTI step headers with 2½" all the way back!

Did i forget something?
Well thats about it! Is my cam to gentle or what could it be thats causing this? Shouldnt the vacuum be like under 10 inches per mercury?

Someone have a good idea?

Thanks in advance!
Chris