no[little] power brakes assist

have power brakes on my car, have fresh not fully broken in 318 with a comp cam, and high dome pistons, have just checked the engine vacuum with the engine warmed up at idle the best I get is 15 for vacuum, when I increase the engine rpms the vacuum does increase to about 18-20 for vacuum, my questions is will the vacuum amount increase as the engine breaks in ? if not I may need to look into a vacuum pump kit so I have good power brake assist. or maybe would a vacuum resiovor help ?