Thank you for your post.
I am unable to replicate the issue using FileMaker Pro 14.0.1 under Mac OS X 10.10.3. I have a layout "populated" layout with tab controls, thumbnail images, fields, buttons, etc. totaling 150-200 objects, and I do not see a delay either through a New Window script step or selecting New Window from the Window menu. What else can you tell me about your layout to help me replicate the issue?