It's most likely not related to the amount of text, as you would need a lot more to cause issues. The performance impact increases significantly when you have lots of small additions to the text rather than one or two large additions to the text. This lag issue is caused by the amount of calculations performed before the text is displayed.
The core of the problem is that sexdescriptions.gd is quite inefficient and does about 50 times as much work as it needs to. Aric increased the number of times it is called from about 4-8 times per action to about 20-26 times per action (per person with 4 participants in the action, so a single action could result in 100 calls). So just the math for a single function suggests that it needs to perform about 4-5 times as many calculations as before. On top of that, Aric has added a large amount of additional calculations which are performed multiple times per action effect.
In effect the number of times the group of calculations is performed is N^2. Meaning that for 2 participants the group of calculations is performed 4 times. For 3 participants, 9 times. For 4 participants, 16 times. For an orgy of 6 participants, 36 times.