Total Protection is probably a resource hog. Nothing you can do about that, except disabling features/components you may not want (software panel, access the SecurityCenter, click on McAfee and check or uncheck what you don't want).
Leftovers of your previous Norton product can also cause problems. Use of the Norton uninstallation tool is recommended, although I don't know how that would go with your current McAfee software. If you decide to uninstall and reinstall McAfee, don't forget to use the MCPR tool plus instructions (can be found on this forum).
Disabling Artemis (called 'active protection', you can find it somewhere in the menu) might also speed things up, but that is not without drawbacks.