What follows is my own opinion, clearly labelled. I have, however, been in computing for over 30 years, and have built countless machines both for personal use, friends, and clients.

It depends on what you do in Poser. If the specs of the laptop do not equal or exceed those of the current computer, you will take a performance hit. Also note, unless all you render is "naked Vicki in a temple" you need AT LEAST 8 gigs of RAM and preferably 16 or more. You're not going to find that in a laptop without paying BIG bucks. Typically, one buys a laptop for portability. That is why they were made. Performance is best served (from a cost-effective standpoint) by a desktop. 

Others will have other opinions. Your mileage may vary.