Hi Amy,
A hot fix is an urgent fix for a specific version. So if there is a hotfix for version 11.5.1 then it is only to repair something in that specific version.
To upgrade your software to the latest version you download the version from new versions in support downloads.
If you are going to update to 11.5 I would wait about a week and download and install version 11.5.2 instead downloading and installing 11.5.1 and then having to do it all over again in a week or so.
Neil