It is probably worth noting that since July 9th this year, just after version 1.6 was released, the number of rules used by Spybot has increased from 176,938 to 340,806 on Nov 26th, an increase of over 90% or nearly double, so it is small wonder that scan times increase for any particular version on any particular platform.
If the number of things you are trying to protect against keeps growing, then the amount of time spend protecting yourself will keep increasing. If you don't update your hardware and software to be able to comfortably handle this extra workload in addition to the work you really want your PC to do for you, then at some stage you will have to decide which catagory will have to be sacrificed.