Nope, no lag. What kid did you buy?
When you apply pedal, that opens a vacuum valve. Push lightly and it opens it slightly. Push hard and the valve immediately opens all the way making it work like a servo valve.
Are you sure you have the booster set correctly to the M/C?
Did you properly bench bleed your new M/C?
Is all air out of the system?
Are all the firewall/booster/master bolts tight? Any flexing will subtract from pedal response. - Dave