Eliminating trunked frequencies will not affect scan speed in any noticeable way (well, unless you eliminate the control channel, in which case it scans much faster).
Eliminating programmed channels (Talk Groups) will not affect scan speed in any way at all.
It will not make it any faster because as the other person said, it only listens to the control channel when passing through. Use control channel only anyways though because it keeps it simple when programming your scanner.
As stated, not much you can do about trunked systems, BUT, you can speed scanning by sorting all of the conventional freq/sys/group in ascending or descending order. This is best accomplished with software.
Eliminating trunked frequencies will not affect scan speed in any noticeable way (well, unless you eliminate the control channel, in which case it scans much faster).