Join our CAD community forums where over 25,000 users interact to solve day to day problems and share ideas. We encourage you to visit, invite you to participate and look forward to your input and opinions. Acrobat 3D, AutoCAD, Catia, Inventor, IronCAD, Creo, Pro/ENGINEER, Solid Edge, SolidWorks, and others.
I would try to pinpoint the exact geometry Solidworks is having issues with. I reckon since you have an old and new model this is some newly added geometry. Then you can decide if this geometry is essential for the simulation. It seems to me you have alot of "unused material" in the part where there is no stress at all (!). It is time consuming to simulate and mesh these useless areas.
So you could also only model the portion that is critical for the stress simulation.