Is there a way to do a non real time preview in after effects?

The Preview should be real time after the frames have loaded into RAM.

You can lower the Frame Rate in the Preview panel for non-real time previews.

You may also find it helpful to use a lower Composition Resolution, to skip frames, and/or adjust the Cache Frames While Idle preference.

When Georges Méliès' started doing animation in 1896, he began with what is called a Pencil Test. Sketches were made of starting and ending poses, and then the in-between poses were sketched with a pencil. These rough sketches could be quickly flipped through to ensure the action works by just binding the pages and flipping through them with his thumb. When the Pencil Sketch was satisfactory, he moved on to the next step: Ink And Paint. The final animation cells were perfected and then photographed, one frame at a time. 

All animation studios today utilize a variation of that Pencil Sketch/Ink And Paint workflow. Pixar sketches out an idea, creates rough geometry, fiddles with poses, and renders the equivalent of pencil sketch tests. Then the final textures, lighting, color grading, sound, and everything else is prepared and rendered in the modern version of Ink And Paint.

You can do the same thing with After Effects. For your Pencil Tests, set the comp Magnification Ratio to 50 or 25%, turn off motion blur and any effects that take a long time to render, and check the timing, motion, and basic effects by running a Ram preview. If the comp is complex and it is taking a long time to render, you can even set the Preview Panel to skip one or two frames. I don't remember the last time I ran a full-resolution, full-frame-rate preview of a complex composition in After Effects. I rely on the Pencil Test.

When the Pencil Test preview works for you, you can turn on all effects, motion blur, and anything else you need to add to verify that things are working at critical parts of your project by moving down the timeline to your Hero frames and ensuring everything is OK. When the Hero frames are OK, Render the comp. 

Here's another workflow tip. AE is not a video editing app. Use it to create shots you can't make in an NLE, then edit your final project, and do the final sound mix and color grading in an NLE, just like Pixar, Disney, Sony, and every other major studio does. I know it sounds like more work to render and then edit in an NLE like Premiere Pro, but it saves time, makes changes much easier, and you end up with a better final product. More than 90% of my comps are under seven seconds, most of the films I produce have effects shots in more than half of the shots, and most of my films are at least a couple of minutes long. Many are over an hour. Unless AE will render a movie I'm trying to make at the rate of 4 or 5 frames a second, I always render my comps and edit in Premiere Pro, Davinci, or Final Cut.

When using After Effects (AE), you might notice that the preview may not always play in real-time like you might expect. Real-time previews are what you usually see in video editing apps - you hit the preview button, and it starts playing right away. However, in AE, the process is a bit different. It first creates a preview in your computer's memory (RAM) and then plays that back for you. You'll see a green line building at the top of the Timeline panel when this preview is being generated.

AE can also save these previews on your hard drive so that if it needs to show you the same preview again, it can simply retrieve it from this saved cache, making things faster.

The speed at which these previews are built depends on both the capabilities of your computer and the complexity of your AE project.

Here are a couple of things you can do to speed up the preview building process:

1. In the Preferences (now called Settings on the latest macOS), you can go to Preferences > Previews. Look for the "Cache Frames When Idle" section and adjust the time delay for when previews are cached during periods of inactivity.
2. Within the Preview panel, you can lower the resolution of the preview (to half, third, or quarter). This means the previews will be generated at a lower quality, which is quicker for your computer to handle. You can even set up different keyboard shortcuts for various preview quality settings.