Do you run any caching plugins? Do you generally do any database optimization? Does your site get a lot of traffic?
These things might have more to do with performance than the number of leads in your table.
The only thing I can think of is that you are checking for some unique entries (no duplicates)? If so, then maybe checking might take an extra little bit of time, but it shouldn't be slowing down too much, even with 20,000 records.
What I would recommend would be to duplicate your form, and use it live without purging any data. This will mean that new submissions won't be tested against your no duplicates test if you have one. See if that has any increase in performance.
Look for tutorials on optimizing a MySQL database, see if your host has any logs related to SQL that could be related to slowing things down. You should be able to have 100x that number of records without seeing much of a performance hit though.
Posted 10 years ago on Wednesday May 30, 2012 | Permalink