There are no obvious reasons why searches would be slower in recent updates so to investigate the issue please collect some concrete figures.
Step 1: Baseline search
Create a baseline search to test the time taken. Run the search 3 times to get an average.
Step 2: Out-of-the-box figures
To remove the impact of any configuration modifications, download and install the current portable version into a temporary folder:
Run the same search as in Step 1 and check that you have the same number of hits. Repeat the search 3 times to get an average.
Step 3: Comparison with an older version
Download and install the portable installer for version 8.5 into another temporary folder:
Run the same search as in Step 1 & 2 and check that you have the same number of hits. Repeat the search 3 times to get an average.
Compare the results
If the results are the same but the times are different then please contact Support for more help.
To narrow down where any increase may be taking place try running the search on plain text files, this separates out the search engine work from the text conversion work. If you don't have a library of text files try switching caching on which will pull the text from the cache instead of using the text conversion routines.