Recently I released a minor update for PluginLoadTimes for QGIS. You can download the most recent version of this plugin from within QGIS, because it is available in the official QGIS Plugin Repository.
If QGIS takes long to start, it is probably because some of the plugins you installed take a long time to load at startup. This plugin shows the latest load time of each plugin (QGIS startup, plugin installation,…). It does not give you information about the speed of plugins when they are used. With the information provided by this plugin you can easily decide which plugins to disable, to make QGIS start faster.