After Effects :: Render Times Of Certain Project Slow Down

i have a certain tv-promo-project where i have to render several comps which all include the same amount of text and just a hand full of additional graphic elements, e.g. a lensflare and a glowing line which separats the text blocks.
 
The text of the specific promo-comps are read out of a "main text comp" by expressions. The expression is as follows:
 
txt = comp("Master Textkomposition").layer("Textebene").text.sourceText;
txt.split("
")[0]
 
The rendertimes of the project are constantly slowing down as the render queue and the process goes on. The first comp takes about 8 Minutes to render (it is only 10 sec long) and the second already 20 min, where the third comp reaches like 2 hours of render time. I also recognized that even the preview in the timeline is really slow, although the used effects are usually not that performance heavy.