The Tories' webpage took 24.78 seconds, according to the study.
Bob Dowson, director at Site Confidence, said the download speed of a site is rated very poor if it takes over 20 seconds to download.
Labour's website took 12.06 seconds to load. Only the Liberal Democrats got the time under 10 seconds with an impressive load time of 6.24 seconds.
The Tories' website was available throughout the month, while Labour's site was down for one hour and 13 minutes. The Liberal Democrats site was down for only four minutes and 19 seconds.