This article addresses potential problems with low frame rates. If you are experiencing increased loading times, please read Loading Time Optimization.
There are several reasons why your frames-per-second rate might be too small, causing single frames to be strongly noticeable.
Enscape is GPU-bound, so you might consider to invest in a faster GPU, e.g. a NVIDIA GTX 980 for a free-flowing experience.
Usually it’s not the project size that is the issue but rather the project containing a lot of fine tessellated geometry such as pipes, cables, and furniture. All this might be overwhelming your computer. Try to hide elements in your project, especially small but detailed things.
You can increase your rendering speed simply by dragging the corner of the Enscape window to make it smaller. This reduces the amount of rendered pixels, increasing rendering speed.