RTL compiler has a default value for input switching activitiy (i.e how fast inputs change)
Directly from the rc-lp manual:
If you want a fast power analysis you can choose to apply the default switching activities.The tool default signal probability is 0.5, the tool default toggle rate is 0.02, and the defaulttoggle rate unit is per nanosecond.
If you simulate your cell using constants as an input, or a very low switching rate, you might get a huge difference. So, either change the input switching activity to what you have set in virtuoso, or do the oposite, and let us know
edit: made response easier to read/understand