You don't say what sort of system you're running on, but if it's a bit old and clunky it will struggle.

Use D3D's render script and start with the settings shown for previewing. Build up from here to get settings for final renders. If you have 4 or more cores, keep your bucket size low to speed things up.

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Windows 10 x64 Pro - Intel Xeon E5450 @ 3.00GHz (x2)

PoserPro 11 - Units: Metres

Adobe CC 2017