8/10 seconds abolutely normal, it's not how long it primes but more that it does, it is working ok.
As for the "leaning out", what makes you think this do you have a guage(AFR) ?
May be wise to change the fuel filter in that case, the AFR at all speeds loads is controlled by chip with trim inputs, a dodgy CTS can do this but would effect it at all times not just at top end.
If you know your car is defo leaning out it can only be lack of fuelling which could be something as simple as a new filter needed or pump/regulator on way out.
tabetha