Will the LoginSecure Framework slow down my website?
Yes but negligible. Depending on what features are switched on a certain amount of files are loaded. For instance, with the Mobile Detect feature, it needs to load the file for this.
We therefore also recommend to always install at least the free version of JCH Optimize(https://extensions.joomla.org/extensions/extension/core-enhancements/performance/jch-optimize/) or use the Pro version which is really worth it! Or use an equivalent extension from another developer(https://extensions.joomla.org/tags/site-performance/).