Hello
1.What type of mesh you are using? Midplane, fusion or 3d?
2. What type of part it is? If its is with lot of thickness variation and geometry complication you may have to use fine mesh, if it is just a flat part, after capturing all the intricate geometries using fine mesh you can even remesh the same model to coarse mesh.
3. With good understanding, you can even conclude running analysis for only half the model. Caution: Holds good for only fill analysis.
4.Switch on only the elements needed to be mirrored. Try pruge nodes and merge options.
Regards
Navam